Request for Recipe (.223 77gr HPBT), also info to share

[new2mud]

Originally Posted by danpass

I've been shooting 77SMK out to 600:

77 SMK
LC case
23 grn XBR 8208
Wolf SRM primer

2.245 COL

RRA NM, 20in, 1/8, SS, Wylde chamber


No chrono data though

Should be right around 2,670 fps with that load. I have almost the same setup, same load, incl. Wolf SRM primers.

[GeoffLinder]

I don't load SMK 77's to very high velocity for my 20" rifles. Accuracy and velocity are not interdependent on their own. You do not need a high velocity to get small group sizes.

Quite often a lower velocity will provide smaller groups downrange IF that velocity matches the bbl node. You will always find more than one bbl node across a good range of velocity so there is no real reason to load to the point of primer piercing.

High muzzle velocity is needed only for maintaining supersonic speed to a longer useful range AND reducing wind drift comparatively.

I typically like to see no more than 2650-2700 fps from a 77gr in a 20" bbl.

My pet SMK77 load goes 2665fps out of my 1:8 JP AR.

Recipe:
24.3gr Varget
LC brass (weight segregated and uniformed)
WW SR primer
2.250" COAL

I put 24.5gr Varget under the SMK69 at 2.245" COAL and get 2700ish fps and same point of impact at 200 yards as the SMK77 load. I like not having to change my scope settings on my multi-gun competition rifle

Here are some groups shot with the SMK77 load in my JP 1:8 20" mid-weight bbl.

BTW, 77gr boattails (VLD's actually) are still wallowing around and not fully spin stabilized at less than 125-150 yards so they tend to group larger than they ought to at 100 yards. 55gr flatbase is your best bet if all you want is the smallest group at 100 yards


10 shots at 200 yards





5 shots at 100 yards

[1lostinspace]

Best load I have found is

winchester brass trip 1.750"
24 gr TAC seat to 2.26"
and use a half turn on a Lee factory crimp die

[Sunday]

You guys are hard core !!! thanks for the info!!!

[ctrmass]

I havent read all 5 pages, but AA 2520 is a pretty good powder for the 77's.
Accurates site has them going 2900 + FPS out of a 24" bbl.

bullet start FPS max FPS psi OAL
"2520 77 SIE HPBT 23.0 2,674 25.5 2,925 62,200 2.260"
This a "nato pressure" load. It dont say but I'd assume a 5.56 chamber.

From their site.
http://www.accuratepowder.com/wp-con...d_data_3.5.pdf

I'm not sure what you'd lose with a tube 4-6" shorter, but it cant be much.

[new2mud]

Originally Posted by ctrmass

I havent read all 5 pages, but AA 2520 is a pretty good powder for the 77's.
Accurates site has them going 2900 + FPS out of a 24" bbl.

bullet start FPS max FPS psi OAL
"2520 77 SIE HPBT 23.0 2,674 25.5 2,925 62,200 2.260"
This a "nato pressure" load. It dont say but I'd assume a 5.56 chamber.

From their site.
http://www.accuratepowder.com/wp-con...d_data_3.5.pdf

I'm not sure what you'd lose with a tube 4-6" shorter, but it cant be much.

For the 77-grain bullets, max load (i.e. fastest) is often not the most accurate. The load listed above is a max load ONLY to be used in 5.56, Wylde, Noveske or other higher-pressure chambers, NOT to be used in a .223 chamber.

Even with a higher-pressure chamber, start lower and WORK up to a given load--never take a max published load and assume it is safe for YOUR barrel.

[ctrmass]

Yea, I figured that. Just thought I'd throw the fact out that they specified it was NATO pressure.
I listed the starting loads just for that reason. I had the post pretty lined up,(bullet start FPS max FPS psi OAL) but when I posted it it went all to hell.
Accuracy will be different in every barrel. Some actually prefer hot loads.

[ctrmass]

Originally Posted by new2mud

Even with a higher-pressure chamber, start lower and WORK up to a given load--never take a max published load and assume it is safe for YOUR barrel.

That's reloading 101. If youre reading this, that should be a given.

I wouldnt suggest anyone start learning about reloading on this specific (MK262 clone) load.

[neal0124]

I'm adding my load using Alliant ARComp powder because I haven't seen any other loads with it.

77gr smk w/cann
22.7gr ARComp (22.5gr out of Lapua brass)
LC brass
CCI 41 primers
Don't know the OAL, I load them max length for my Cproducts mags (which will also fit in pmags)

Shooting out of a 18" superior barrel with a wylde chamber and 1/7" twist.
I don't shoot for groups but when I have I've gotten sub-moa with this load, around .9 moa. I've shot this at 1000 yards using 52moa elevation and can hit a 20"x18" at about a 80% hit ratio. I've never shot this over a chrono so I have no idea what the velocity is.

[Quinc]

Chrony'd my first loads and thought I would add them. Chrony was about 4ft in front of barrel.
AR15 w/26" WOA Upper

77gr SMK HPBT
Reloder 15 22gr -OAL 2.26" - Lake City '11 - Average FPS 2588 (10 rounds)

Varget 23gr - OAL 2.26" - Lapua - Average FPS 2706 (10 rounds)

[Leatherneck07]

It's cool to see that I am not alone in the quest for reproducing this amazing round. I've recently produced a few of my own. I too am using RL-15 and TAC. As these seeem to be the closets powder to what is being used. apparaently RL-15 is acctually specified for the m-118.

my first run of Nosler CChpbt in 77 grain was backed with 23.0 grains of RL-15. I loaded them to a col. of 2.25" the chronographed out of a 16" carbine at 2614 I believe. but, I have changed that recipe and my manufacturing process all together.

I have a dillion RL-550B and a single stsge RCBS for sizing and trinimng with a Dillion rapind trim 1200. It allowed me to get the cases to very tightghtly trimmed tollerances and fast. After trimming then some brass needed primer crimp removal. done, using the Dillion superswage 600. easy. then every case needs to have the case chamfered for theses VLD style bullets. alot of work. But, now I have uniform brass!

So, that brings to me to what I am currently working up.

last night after careful thought of Noslers recipie for the 77 grain CCHPBT and TAC ma charge of 23.5 grains. I chose to back up to 23.2 grains. I am trying to get near the magic velocity of 2750 to 2800 fps. That seems to be the speed where most of the match and sniper ammo is produced.

so: 77 grain Nosler CCHPBT over 23.2 grains of TAC CCI 400 primmer mixed headstamp brass trimmed and chamfered to 1.75" and COL of 2.252 I will let you know how they group and velocity etc.

Next up I am going to losd the Sierra 77 grain MK over 24.5 grains of TAC and same COL.

The Sierra bullet definitely has a different profile so the must be where the difference in speed comes in. Also Ramshot has a recipie list for new NATO pressures above 62350 PSI. Thier max load shows 24.8 grains of Tac. So, I am backing off a half grain. but according to thier recipies I should still get the velocity I am looking for. The Sierras. manual has 24.0 as thier max. So we will see. I like my riffle and don't neccesarily want to be pushing max loads through it all the time.

Anyway good luck. I look forward to hearing which losd works for you. I havn't even touch on the loads I plan on working up for RL-15. the first stuff I made was shootin dme sized 10 shot groups through an ADAMs Arm Carbine upper with a twist rate of 1-7". Can't wait till it is broke in. I think I'll tryu a match.

[BrianRodela]

If your looking for a velocity for the 262, my dope for Oceanside area is

100 yd zero
200 yd- 1.5 moa
300 yd- 4 moa
600 yd- 14 moa

Work it backwards and you might find how far off some of you are on your velocities. The round shoots very well and doesn't show any over pressure signs.

[SWammo]

This is one of the rounds that got our company going.
Initially, as a garage handloader, I worked with up to 25 grains of Varget in Military brass. Around 24 grains was good for 5.56 pressures. Anything more, and primers started to pop occasionally.

As as a commercial loader, we've had success with Varget, H4895, and IMR 8208 XBR. The latter we switched to early, and have had great results with.

For MK262 type performance, i recommend starting around 23.2, and working up to 23.8 grains. We seat these at 2.250 max COAL, in military brass, with a CCI military or #450 primer. This is what we load our match ammo with, and it is outstanding. Our sponsored shooter used it along with our 308 to win the Summer Mammoth Sniper Challenge in 2011.

This is for 223 Wylde or 5.56 chambers only

[Quinc]

Originally Posted by SWammo

This is one of the rounds that got our company going.
Initially, as a garage handloader, I worked with up to 25 grains of Varget in Military brass. Around 24 grains was good for 5.56 pressures. Anything more, and primers started to pop occasionally.

As as a commercial loader, we've had success with Varget, H4895, and IMR 8208 XBR. The latter we switched to early, and have had great results with.

For MK262 type performance, i recommend starting around 23.2, and working up to 23.8 grains. We seat these at 2.250 max COAL, in military brass, with a CCI military or #450 primer. This is what we load our match ammo with, and it is outstanding. Our sponsored shooter used it along with our 308 to win the Summer Mammoth Sniper Challenge in 2011.

This is for 223 Wylde or 5.56 chambers only

Any tips on loading precision rounds in volume? Just doing the powder and seating the bullet takes me about 2-3+minutes each round.

[ExtremeX]

Awsome thread.

Has anyone tried the SMK 77g w/c with BL-C(2) ???

All I have on hand right now is H335 and BL-C(2), and just got my first small pack of 77gr SMKs.

[Quinc]

Originally Posted by ExtremeX

Awsome thread.

Has anyone tried the SMK 77g w/c with BL-C(2) ???

All I have on hand right now is H335 and BL-C(2), and just got my first small pack of 77gr SMKs.

I am convinced that the 77gr SMK's are crap. I cannot get them to group for sh*t compared to Nolser bullets. Even my 69gr Nolsers group better then the smks out to 500yards..

[ExtremeX]

Originally Posted by Quinc

I am convinced that the 77gr SMK's are crap. I cannot get them to group for sh*t compared to Nolser bullets. Even my 69gr Nolsers group better then the smks out to 500yards..

There is a strong chance your rifle just doesn’t like them…

I only got a small box of 50 to try; I think I’ll load em up with BLC2 and try em out.

I actually hope the Hornady 68gr Match ammo I loaded up shoots really well, they are cheaper than the SMKs and I like that. I haven’t tried any Nolser bullets. Want to do a little trading?

[W.E.G.]

Velocity duplicates of Black Hills 77-grain “blue box” according to Quickload
(scroll down for chart)

Black Hills 77-grain “blue box” ammo consistently chronographs about 2710 fps through the rifle I use for all my AR15 ammo testing.

Quickload
These loads were determined by Quickload version 3.6.
http://www.neconos.com/details3.htm
Quickload is a fairly expensive computer program for reloaders.
Quickload has been around in various forms since 1987.

Comparison history
The only load listed here, and actually tested over a chronograph, is the load for TAC powder. For all intents and purposes, TAC provided a velocity identical to the velocity obtained from Black Hills “blue box” 77-grain ammo with the Sierra 77-grain MatchKing bullet. Moreover, the powder I inspected from an actual 77-grain “blue box” cartridge weighed exactly 23.9 grains, and had an appearance exactly like Ramshot TAC powder.

Quickload consistently predicts about 90 FPS faster velocities than actually obtained over a chronograph.
Based on my empirical testing of various loads over the chronograph, and comparing the chronographed velocities of those various loads, I have discovered that Quickload routinely predicts a velocity 80 to 100 feet per second faster than the velocity actually obtained by chronograph measurement when the ammo is fired in an AR15 type rifle. My theory for the consistent velocity discrepancy is that Quickload does not account for the loss of pressure due to gas escape through the AR15 gas port.

Black Hills 77-grain “blue box” ammo consistently chronographs about 2710 fps through the rifle I use for all my AR15 ammo testing. Similarly, 23.9 grains of TAC provides the same velocity with the same bullet. Quickload suggests that 23.9 grains should generate 2807 fps from an un-ported 20-inch barrel. Based on this consistent discrepancy, I have selected for my investigation, loads modeled by Quickload which also are predicted to be in the approximate 2800 fps range.

Magazine-length dimensions
All Quickload modeled loads assume bullet seated to 2.250” overall cartridge length.
SAAMI specification maximum length is 2.260”
I find that ammo loaded to SAAMI maximum length will sometimes be just a bit too long for AR15 magazines.
Ammo loaded to 2.250” or less never causes a feed-malfunction due to excess length.

Pressure info
The SAAMI industry specification for 5.56 NATO ammunition is 62,366 maximum PSI.
According to Quickload, all loads listed in the following chart fall below SAAMI maximum pressure, at 70 degrees temperature. This modeling exercise does not attempt to account for any variations which may occur due to temperature.

Disclaimer
This information is provided only for educational purposes. None of these loads are specifically recommended for any particular, or general, purpose. Persons using this information to construct live ammunition do so at their own risk, and with the understanding that this information may not be accurate, and that the result of use of this information may result in damage to property or injury to person.

[East Bay Cop]

I havent loaded 77 grs yet, heres my current combo...

69 gr Sierra match bt hp, 23.5 grains of H335, CCI primers and winchester-lake city brass.

[Mark I]

So I won 1000 of Nozzy's 77g projo's at the Crimson Trace Midnight 3 Gun match last month, and I've also been trying to figure out how to do a Mk262 clone load. The heavier 77g projos do much better on knocking down steel than the 55g pills. I noticed that CFE223 tends to show higher velocities in Hogdons data charts than the other usual powder selections. "Hmmmmm..." says I. "Higher velocities before reaching max pressure in almost any given bullet weight..."

Yes, Hodgdon only lists a 53,500 psi SAMMI load that max's out at 24.3 grains for a reported 2811 fps (apparently from a 24" bbl), but I'm not afraid to experiment with slightly "+P" loadings of the CFE223 in my mil-spec guns. If Hogdon had published NATO spec 62,500 psi loads like Ramshot does, I bet CFE223 would be prominantly displayed. If uncle sams guns can do 62,500 PSI, so can mine. Increasing .2-.3g at a time, I was able to get the following results from a 14.5" carbine, and a 20" HBAR. Both chrome lined 1/7 twist 5.56 chamberings, using LC brass and CCI "5.56 military" primers, 2.25" COL. 5 shot strings, barrel was warm to touch, ambient temp 92 degrees, chrono 10 feet from muzzle.

CMMG M4- 24.3g = 2525 fps av, 24.6g = 2580 fps av, 24.8g = 2618 fps av, 25.0g = 2654 fps av, 25.2 = 2675 fps av.

Colt AR15A2 HBAR- 24.3g = 2650 fps av, 24.6g = 2740 fps av, 24.8g = 2790 fps av, 25.0g = 2834 fps av, 25.2g = 2890 fps av.

I read, and re-read all the helpful comments here before proceeding, and appreciate all the work that you guys have done. Now obviously you are proceeding at your own risk with loads that are 4-5% above published max if you choose to follow this path. Your mileages may vary! Just to be clear, I DID NOT START WITH +P LOADS. MY STARTING LOADS WERE 5% BELOW MAX TO CONFIRM THAT NO PRESSURE SIGNS WERE PRESENT BEFORE PROCEEDING UP TO THE "+P" NATO'ISH PRESSURE LEVELS. I did not do any chrono or other data collection at the lower levels, as that was not the intent of my endeavour. I do not have a pressure transducer, but have unfortunately peirced my fair share of occasional primers in over pressure .223 service rifle / 3gun loads over the last 35 years. Not proud of it, just giving reference that I recognize the over pressure signs listed below when I exceed them. "Good judgement comes from experience, and experience usually comes from bad judgement."

As far as range notes on this session; much of what has already been discussed applies. The comments about the repeatable measured weight of CFE 223 are correct. This stuff meters like water! I never threw even a .05g variation in weight from my RCBS measure. Best accuracy was in the 1-1.5 MOA department, and was with the lower velocity loads (24.3g -24.6g = 2525-2700 fps). Groups opened to 2.5" at 25.2g. Groups were fired with 4x optics, comparable to the ACOG's in use today (so theres likely a bit better accuracy possible with a higher magnification optic used on Mk 12 clones). Not a single sign of over pressure was detected all the way up to and including the 25.2g load in either rifle. I had reached my velocity goals, and accuracy was deterriorating, so I did not persue it further. No flattend/cratered/peirced primers, no scuffed ejector marks, no incipient case head seperation ring, no split case necks. I used 3X fired LC 85 cases. I used sorted cases with a slightly heavier weight (94g deprimed) to push the limits of the smaller case capicity / higher pressure envelope. Muzzle blast and felt recoil were noticeably higher after 24.6g loadings. All rounds were magazine fed and functioned 100%, and brass was deposited on the deck at 4 o'clock about 5 feet out. It appears that in MY guns, the clone load for the M4 is going to be 24.7g of CFE223, and 25.0 for the A2 based on reported Mk262 velocitys in Jicko's OP. However, due to the lower accuracy produced there, I will be using loads in the 24.5g - 24.6g range.

Listed velocitys of spec Mk262 are:
14.5" 2576 FPS
16" 2669 FPS
18" 2769 FPS
20" 2818 FPS

So to summarize: I pushed the envelope with CFE223 by over loading by almost 5%, using heavier weight cases, shot in hot weather, and got away with it. Inventory reveals 10 fingers, 2 eyes, and all bodily fluids accounted for. Probably the most useful information I take away from this experiment is that IN MY GUNS there is going to be AT LEAST a .6g+ margin of safety before I reach over pressure loads when I shoot the 24.6g loads. I will likely load some of the 24.8 loads and try them at 300 yards to check accuracy, since the longer "VLD" type bullets (its hard for me to call a .34 BC projo "VLD") have a tendancy to not fully stabalize until the 150-200 yard mark. But given the 2"-2.5" I got at 100, I don't hold out much promise. Remember speed is fine, but accuracy is final.

[Quinc]

Originally Posted by Mark I

So I won 1000 of Nozzy's 77g projo's at the Crimson Trace Midnight 3 Gun match last month,

I pushed the envelope with CFE223 by over loading by almost 5%, using heavier weight cases, shot in hot weather, and got away with it.

What do you think of the Nolsers vs the SMK? So far I have found the 69 and 80gr Nolsers kick the sh*t out of sierras, but I haven't tried the 77's yet.
Also was your barrel any cleaner after shooting with CFE223?

[Mark I]

I don't notice its any cleaner in the carbon fouling department, and I'll run some Sweets down the bore to see what blue I can scrub out (if any) later on. I have an 80g SMK load that uses 4895 for my 600 yard line that absolutely shoots X ring all day. I have sent hundreds down range over that load and love it. This is my first time running the Nozzy's, and I'm not unfavorably impressed. They were shooing 1 moa with my lighter loads, and basically "0" load development since all I was going for was a Mk262 clone load with the CFE223. I cant help but think that if I was to work with several powder/primer/brass combos, I could probably get a very nice load. I would like to see if it hangs in there at the 300 line. I used the 75g Hornady's for a time at the 200 and 300 lines, but the results were mediocre at best out of my guns. 69 SMK's always did fine by me there, so I stayed with them after the 75g supply was expended.

Attached is a 5 shot group I shot last month with my 80g SMK load at 100, just reconfirming my zero's after a barrel change out. I think it was .4 CTC! Strange that the big ol' 80g had already "gone to sleep" and become stable in flight at the 100 yard line, but thats probably why its so dead nuts on out at 600!

[sigma6]

As a general rule is it better to use Nato brass or .223 brass for MK262 clones?

[curisu]

Found this doing some light bedtime reading on Fr. Frog's "Care and Feeding of the AR15/M16 Rifles" page.

Immediately thought of this thread/sticky and thought it may be useful to anyone still developing a clone:

MK262 Mod 0/Mod 1 (These are believed to be the actual specifications)
77 gr Sierra MatchKing (Mod 1 is cannelured lightly); Velocity 2780+/- 40 @15' SD<= 30
Pressure 58.7 Kpsi (piezo), or Avg + 3 SD <=64.7 Kpsi
Port pressure Avg -3 SD >= 15.3 Kpsi
Propellant RL 15 (chrg unk) or non-canister TAC 24 - 25.5 gr (adjusted to give spec performance)

MK362 Mod 0/ Mod 1 (Currently experimental - works in 1:9 twist bbls)
75 gr Hornady BTHP (Mod 1 is cannelured lightly); Velocity 2800+/- 40 @15' SD<= 30
Pressure 58.7 Kpsi (piezo), or Avg + 3 SD <=64.7 Kpsi
Port pressure Avg - 3 SD >= 15.3 Kpsi
Propellant RL 15 (chrg unk) or non-canister TAC 24 - 25.5 gr (adjusted to give spec performance)

For the MK262/362 equivalent handloads TAC, RL15, AA2230, H335, and H4895 appear suitable with TAC looking the best

[Hoop]

Originally Posted by sigma6

As a general rule is it better to use Nato brass or .223 brass for MK262 clones?

Use whatever brass you can get your hands on. I like LC and Rem.

24 TAC + 77 @ 2.245 is closest I got in LC brass.

You are much better off picking a more temp stable and accurate powder like varget H4895 etc and developing a good load than trying to clone the mythic Mk262.

[mroels]

Originally Posted by Quinc

What do you think of the Nolsers vs the SMK? So far I have found the 69 and 80gr Nolsers kick the sh*t out of sierras, but I haven't tried the 77's yet.
Also was your barrel any cleaner after shooting with CFE223?

Are you guys shooting the 80gr's out of ARs? Can the 80gr's Nosler or SMKs be seated to mag length? Or is it single load only?

[Quinc]

Originally Posted by mroels

Are you guys shooting the 80gr's out of ARs? Can the 80gr's Nosler or SMKs be seated to mag length? Or is it single load only?

I used a hornady OAL gauge and seat at various lengths off the lands usually around .001 - .003". The length of the round from primer to bullet tip averages around 2.39ish. So you have to single load them.

[Mark I]

Originally Posted by mroels

Are you guys shooting the 80gr's out of ARs? Can the 80gr's Nosler or SMKs be seated to mag length? Or is it single load only?

I load them 2.5-2.55" for service rifle competition. Definately single load territory.

[pardou]

cheapest range ammo recipe?

[Mark I]

Originally Posted by pardou

cheapest range ammo recipe?

Dedicated .22 LR upper or a complete AR-22 platform. Just shoot smaller targets closer in. All samey-same: sight alignment/trigger control/sight picture. At a savings of .50 cents a round over "cheap" 55 fmj ball, .22 LR will pay for that upper or M&P15/22 in less than 1000 rounds... Thats only 2 bricks worth of trigger pulls y'all!

[FMJBT]

Got some interesting results from the last trip out to the desert. Taking notes on bullet drop for various loads at 650 yards, I've reverse engineered the drop using the android app "Shooter" to come up with a velocity for the loads.

My standard load is 23.8 grains of Ramshot TAC in LC brass using a Nosler 77 grain CC seated to 2.25" COAL. Primers are CCI #41. At 650 yards, my drop for this round is 5.5 mils at an elevation of 1500 FT. This gives a velocity of around 2710 FPS according to the "Shooter" app.

I loaded up another batch of basically the same round, only using 24 grains of Hodgedon CFE-223 in place of the 23.8 grains of TAC. These rounds were only dropping 5 mils at 650 yards, with a muzzle velocity of around 2820 FPS if the app is correct. Pretty impressive numbers out of an 18" barrel.

For both of these loads, I worked up until I began to see flattened primers, then backed off 1/10 grain for the final load, so these are both right at the the threshold for showing pressure signs out of my SPR. I definitely wasn't expecting to see such significantly higher numbers out of the CFE load. I think the next test will be to try the CFE powder with the slightly lighter 75 grain Hornady HPBT's to see how fast they can be pushed out of an 18" barrel. The Hornady bullets have a better BC than the Nosler (.390 vs .340), so it should add quite a bit to the usable range of the rifle.

[ar15barrels]

Originally Posted by FMJBT

For both of these loads, I worked up until I began to see flattened primers, then backed off 1/10 grain for the final load.

If you develop loads at 60 degrees, they are going to be a lot hotter when it's 90 degrees.
Make sure to re-work your loads this summer as your winter loads will not be the safe when it's 30 degrees warmer...

[FMJBT]

Originally Posted by ar15barrels

If you develop loads at 60 degrees, they are going to be a lot hotter when it's 90 degrees.
Make sure to re-work your loads this summer as your winter loads will not be the safe when it's 30 degrees warmer...

Good point. I'm pretty sure the TAC load will be okay, as I worked that one up during the summer last year when it was 90+ out there.

It was about 75 to 80 when I took the CFE loads out there last weekend. I'll definitely be monitoring them closely as the weather warms up. I've heard that CFE is pretty temperature stable as far as ball powders go, but I'll need to see that for myself.

[xrMike]

Originally Posted by Hoop

24 TAC + 77 @ 2.245 is closest I got in LC brass.

You are much better off picking a more temp stable and accurate powder like varget H4895 etc and developing a good load than trying to clone the mythic Mk262.

One thing about TAC... It's NOT very temperature-sensitive according to Ramshot's ballistics people, who say they've tested it at -40F and +140F, and the deviation between those 2 extremes is less than 3%.

[ar15barrels]

Originally Posted by xrMike

One thing about TAC... It's NOT very temperature-sensitive according to Ramshot's ballistics people, who say they've tested it at -40F and +140F, and the deviation between those 2 extremes is less than 3%.

I wishi could do all my shooting in a laboratory environment...
I have not found anyone able to replicate such low temperature sensitivity in the real world.

[xrMike]

Originally Posted by ar15barrels

I wishi could do all my shooting in a laboratory environment...
I have not found anyone able to replicate such low temperature sensitivity in the real world.

Good point. And I know you do a lot more shooting than most of us, so I pay attention to what you say.

Another thing I read online was that the military chose TAC for their 77 grain OTM rounds because it showed only HALF the temperature sensitivity that their spec called for (in addition to meeting their performance requirements), and they were concerned about temp. sensitivity since that ammo would be used in both Iraq AND Afghanistan.

Again, this is something I read online. It could be Internet B.S. but I'm just throwing it out there. It does NOT equal real-world experience, which you have.

All I can say in my limited experience with TAC is that my zero does not change in 45 to 85 degree weather. But that's only at 100 yards. Which is a distance that I know you laugh at, Randall.

[ar15barrels]

Originally Posted by xrMike

All I can say in my limited experience with TAC is that my zero does not change in 45 to 85 degree weather. But that's only at 100 yards. Which is a distance that I know you laugh at, Randall.

Shoot some groups at 600yds.
Record the hard dope and weather conditions on 3-5 different days that you shoot the groups.
Use a ballistic calculator to reverse engineer the velocities, taking weather conditions into account for each day.
You will learn how much dope difference the weather makes and how much velocity difference the temperatures make...

On a hot day, keep some ammo in the shade and leave some out in the sun to bake.
Get dialed in at 600-800 yds and then switch between the two batches and see how much the elevation changes in the same weather conditions when the only change is ammo temp.

It's eye opening stuff for sure!

[FMJBT]

Dwell time of the round in the chamber can also have a significant impact on powder temperature, especially in semi autos after long strings of fire.

[ocabj]

During the 600 yard slow fire prone stage I will usually:

1. Fire the shot.
2. When target comes down, I'll record the previous shot score and location on my data sheet.
3. I will then take a round and put it in the ejection port and let it sit loose over the SLED/magazine.
4. I'll look down range until the target comes up.
5. When target comes up I'll look through my spotting scope, check shot location and score, note the mirage (make a wind adjustment if necessary) and then roll into my stock.
6. When I'm stocked, I'll start the round into the chamber with my finger and then drop the bolt by pressing the bolt catch lever.
7. Then I'll take my shot in about 10 seconds.
8. Repeat

This usually minimizes the amount of time the round is baking in the chamber.

BTW: This is with an AR.

[ar15barrels]

Originally Posted by FMJBT

Dwell time of the round in the chamber can also have a significant impact on powder temperature, especially in semi autos after long strings of fire.

All the more reason to shoot a bolt gun...
You get to control chamber dwell time by not loading rhe chamber and closing the bolt until a few seconds before you are ready to fire.
Those damn magazine-fed autoloaders make the assumption that you are firing quickly as they put a new round in the chamber right after you fire each round!