Will there be a difference - seating depth

[gemini1]

From another post here and at THR, I figured out the OAL from bolt face to lands(?) of my 16" 5.56 upper, it measured 2.367

The test loads I've been doing so far are at 2.250 +/-
So my question is, if I seat the bullets higher or say I go to max at 2.260, is there going to be any change in pressure/velocity and in accuracy?

If it matters, I'm loading 62 gr solid lead core from Evergreen (generic), H335 and Tula primers.

Thanks.

[Bill Steele]

From another post here and at THR, I figured out the OAL from bolt face to lands(?) of my 16" 5.56 upper, it measured 2.367

The test loads I've been doing so far are at 2.250 +/-
So my question is, if I seat the bullets higher or say I go to max at 2.260, is there going to be any change in pressure/velocity and in accuracy?

If it matters, I'm loading 62 gr solid lead core from Evergreen (generic), H335 and Tula primers.

Thanks.

If I am reading your post correctly, you currently have a jump of about .117" when you load that bulllet to 2.250". If you load out another .010" you will likely not see much in the way of changes (pressure/velocity wise). Whether being .010" closer to the lands (less jump) will help with accuracy, my guess would be likely not, it just isn't enough difference.

It is pretty tough to get much advantage in accuarcy with jump distance if you are loading around magazine lengths, at least with a gun with a longish throat. Some guys that shoot bench rest load so their bullets are at or in the lands. This will increase pressures. It also may not help your accuracy. If the barrel is not perfectly aligned to the action, a jump may be preferable to no jump. Getting the jump perfect for your gun is just another loading exercise, but again with a long leade and magazines, sometimes that is one of the load criteria that might be more work than will likely be rewarded.

Also, when you measure the jump, that is bullet specific. A bullet with a different ogive might return a different seating depth to the lands.

I sure hope I read you original question correctly....

[GeoffLinder]

Max OAL for an AR is limited by length that will fit in magazine. This about 2.260"

Best to stay just under that, say 2.250-2.255, BUT you only want to load this long if you are using heavy bullets of 68gr or heavier. For 62gr and under I would recommend you load at 2.230 to 2.245.

As OAL increases, pressure will drop slightly and so will velocity, how much is not a set amount. Only testing will tell you the velocity drop.

Whenever you reduce OAL, pressure rises so you should drop powder charge a few percent. From 2.260 to 2.240 I would drop at least 5% and then carefully work back up or just stay there if velocity is what you want.

Loading to be closer to the lands in an AR is not easily done because of mag length limit.

[gemini1]

Thanks for your inputs Bill & Geoff. Yes Bill you read my query right.

One last question. Is it possible to obtain optimum velocity at loads lower than published max?
I already found the sweet spot load for my 16" 1/7 barrel, its 24.2 gn of H335 on a 62 gr solid lead core Everglades bullet. I'm trying to get the 2nd sweet spot at higher load (for longer distance shots).
Ive loaded 24.6, up to .9 at .1 gn increment. Shot all of those and did not see any pressure signs on the casings nor any problems with extractions. But a fellow calgunner, using quickload, told me my 24.6 h335 load on a 62 gr solid lead core gave a reading of 56,907 psi, over the SAAMI limit of 50,000 psi.
I was told that Speer shows a max of 25 gn for 62 gr using H335.

[Bill Steele]

Thanks for your inputs Bill & Geoff. Yes Bill you read my query right.

One last question. Is it possible to obtain optimum velocity at loads lower than published max?
I already found the sweet spot load for my 16" 1/7 barrel, its 24.2 gn of H335 on a 62 gr solid lead core Everglades bullet. I'm trying to get the 2nd sweet spot at higher load (for longer distance shots).
Ive loaded 24.6, up to .9 at .1 gn increment. Shot all of those and did not see any pressure signs on the casings nor any problems with extractions. But a fellow calgunner, using quickload, told me my 24.6 h335 load on a 62 gr solid lead core gave a reading of 56,907 psi, over the SAAMI limit of 50,000 psi.
I was told that Speer shows a max of 25 gn for 62 gr using H335.

Most of the rifles I have loaded for have more than one node (sweet spot where groups settle down) for a given bullet, etc. So you might find a load higher up. I don't load for .223, so I am the wrong guy on max .223 loads. Geoff or someone else can probably tell you where the likely limit is for that bullet.

[gemini1]

Thanks Bill.

Waiting for Geoff, or any of the seasoned reloaders.

[GeoffLinder]

Thanks for your inputs Bill & Geoff. Yes Bill you read my query right.

One last question. Is it possible to obtain optimum velocity at loads lower than published max?
I already found the sweet spot load for my 16" 1/7 barrel, its 24.2 gn of H335 on a 62 gr solid lead core Everglades bullet. I'm trying to get the 2nd sweet spot at higher load (for longer distance shots).
Ive loaded 24.6, up to .9 at .1 gn increment. Shot all of those and did not see any pressure signs on the casings nor any problems with extractions. But a fellow calgunner, using quickload, told me my 24.6 h335 load on a 62 gr solid lead core gave a reading of 56,907 psi, over the SAAMI limit of 50,000 psi.
I was told that Speer shows a max of 25 gn for 62 gr using H335.

Bill is on the money about there being more than one sweet spot (barrel node). The best barrel nodes to use are almost always not the ones you find at the highest safe pressure velocities. I never load for max velocity anyway (primers just flowing) although I do like to know where that point is for a specific combination of components.

Brass life is better at more moderate velocity anyway. For reference, I like to stay at or under 3150fps with 55gr in .223. I limit things to about 2850fps with the SMK 69gr and under 2700fps with the SMK gr. These are all with 20" barrels, you will typically get 100-150fps less in a 16" bbl than in a 20". When I run charge ladders to find the sweet spot I start at a 10-15% less than max listed load and work it up .2 grain at a time until I get serious primer flow, then I stop and toss the untested higher charge ones in my junk box for later bullet pulling.

I just plain don't like to load to the ragged edge unless I am going for max wind drift resistance at extreme ranges (higher velocity shortens flight time and the lower the flight time, the less wind drift you get). I am talking about 500+ yards here, not below that.

FYI, the 60-62gr projectiles are not a fantastic long distance bullet choice anyway. Figure them for 300-350 meter range usability. Want to shoot further than that and avoid wind perturbance then you should step up to a 69gr plus projectile.

Many folks load to the edge for reasons that quite often elude logic for me (blindly duping a military loading, equalling a published book figure, etc...), but why beat the rifle and your brass up unnecessarily in the quest for something that really doesn't matter IMHO

BTW, I never bother with quick load calcs, That's lab stuff that rarely applies in actual practice. IMHO, level of primer flow is what really matters when determining safe max load for YOUR component and barrel/chamber combination (primer, bullet, case batch). Every case is different (all pun intended). OAL drastically effects pressure too. I always load as long as possible for a given bullet profile.

[gemini1]

Thanks Geoff.
Is it possible to have over pressures on loads lower than recommended max (24.6 vs max of 25 gns), if the OAL is at or close to what manuals state (2.250-2.255 vs 2.260)? The projectiles I used are even shorter than the M855 steel cored ones by 0.98" which means seating depth may not even be as deep as the mil specs ammos(?)

[GeoffLinder]

Thanks Geoff.
Is it possible to have over pressures on loads lower than recommended max (24.6 vs max of 25 gns), if the OAL is at or close to what manuals state (2.250-2.255 vs 2.260)? The projectiles I used are even shorter than the M855 steel cored ones by 0.98" which means seating depth may not even be as deep as the mil specs ammos(?)

Absolutely! There is no way a recipe from a loading manual will ever be what you get in YOUR rifle barrel/chamber and YOUR brass even if seating depth is same and bullet is same. Bullet profile can also be different even if basic weight is same so OAL at same does not mean base of bullet is at same depth. Cases from different manufacturers and even batches within a specific manufacturer will also have different internal volumes.

Peak pressure with a "specific" powder (not all powders burn at the same rate, but this is another story) and charge weight is almost entirely controlled by two things, 1st, internal case volume. This is controlled by how much metal is left inside by different Mfgr's. Even if case outside dimensions are all the same, internally there may be more or less meat in the case web area and so on. 2nd, seating depth (this is not necessarily OAL). Seating depth is where the base of the bullet is at in the case neck not always the OAL.

As an example of case volume variance, take 20 cases from a random sample of range pick, size and then trim them so length and external dimensions are the same, then weigh them, you will typically find up to 2-3 grains of weight difference across brands and up to 1.5-2 grains difference even in same batch from one Mfgr. Almost all of this weight difference is on the inside of the case and effects the volume.

Add to that the variances in chamber/barrel leade (where the bullet is stuffed into the rifling) and small barrel diameter variances, then add slight differences in bullet diameter and construction that effect the compression rate of the bullet as it is stuffed into the rifling AND where the bullet base is in the case neck regardless of the OAL and you will begin to see how pressure can be all over the place from published or calculated empirical data based on a powder, bullet weight and OAL in a generic rifle barrel.

This is why I advise to pay attention to primers when looking for safe pressure range. Also use a chronograph and monitor velocity too. If you are not getting any primer flow, yet a 55gr is going downrange at 3200fps plus you might be nearing max range for that combo of stuff even if primers are not showing issues yet.

Pressure is entirely controlled by YOUR combination of powder charge, barrel/chamber dimensions, case volume, bullet choice and seating depth, NOT by a book or a pressure calculator

Hope this helps :-)

More about powder burn rate (i.e., your powder choice) and it's effect on the initial pressure peak spike at another time

[gemini1]

I'll just stay stick to the sweet spot at lower load, till I get a chrono.
Thanks again Geoff.