bolt lug contact area

[AreWeNotMen?]

The attached photos (crappy cell pics) are of the three bolt lugs on my thus-far lightly used Ruger RPR in 6.5 Creedmoor. I applied red Sharpie to the rear of the lugs, then worked the 60 degree lift up and down while applying rearward pressure.

I pleasure shoot 100 to 1000 yards (mostly around 300), and only do local PRS-style matches very occasionally (i.e., I don't shoot competitively).

Questions:

• Is this contact good/uniform enough?
• If not, how exactly do I lap them? (grit# and base - exact brand and spec would be nice, how much between re-checking, how to best clean up the lug area in chamber, etc)
• Does lapping change headspace?

Thanks.

[baih777]

Do not try and smooth that flush.
What you cant see are the opposite side in the receiver.
You need a gunsmith with proper tooling to get both sides flat .
It will affect headspace.

Even if you try lapping compound . It will change headspace.

[baih777]

You have a Ruger RPR.
The barrel is mounted like a AR . Like a AR barrel extension.
It has a collar on it. You can not adjust the barrel headspace like a Savage rifle.
If you mess up. You would have to order a new barrel with a short throat and have to have the barrel headspaced .

[67Cuda]

I'm no expert, but it looks like it getting good contact on all three lugs. Why are you even looking at this?

[kcstott]

Do not try and smooth that flush.
What you cant see are the opposite side in the receiver.
You need a gunsmith with proper tooling to get both sides flat .
It will affect headspace.

Even if you try lapping compound . It will change headspace.

It will change headspace. but it won't change it enough to measure. and if it does you got way too carried away or used way too course of lapping compound.

[kcstott]

The attached photos (crappy cell pics) are of the three bolt lugs on my thus-far lightly used Ruger RPR in 6.5 Creedmoor. I applied red Sharpie to the rear of the lugs, then worked the 60 degree lift up and down while applying rearward pressure.

I pleasure shoot 100 to 1000 yards (mostly around 300), and only do local PRS-style matches very occasionally (i.e., I don't shoot competitively).

Questions:

• Is this contact good/uniform enough?
• If not, how exactly do I lap them? (grit# and base - exact brand and spec would be nice, how much between re-checking, how to best clean up the lug area in chamber, etc)
• Does lapping change headspace?

Thanks.

The rifle is fine. but you may want to fix the loose nut behind the bolt.

[ShaunBrady]

You have a Ruger RPR.
The barrel is mounted like a AR . Like a AR barrel extension.
It has a collar on it. You can not adjust the barrel headspace like a Savage rifle.
If you mess up. You would have to order a new barrel with a short throat and have to have the barrel headspaced .

It's actually more like a Savage than an AR in that the lugs are in the action, the barrel tenon is threaded and the headspace is set/locked with a nut. The flange on the lock nut is AR pattern.



Bits above are Gen 1. Bits below are Gen 2.

The collar on the barrel hasn't been used since Gen 1 where it was used to provide a stop for the handguard mounting nut.

Prefits are available and the nuts are used to set the headspace.

[ShaunBrady]

[*]Is this contact good/uniform enough?

Yes

[*]If not, how exactly do I lap them? (grit# and base - exact brand and spec would be nice, how much between re-checking, how to best clean up the lug area in chamber, etc)

Just don't.

Similar to setting up an engine, bench clearances are not running clearances. What you see there is the contact that results from the bolt under the influence of the cocking piece and cranked by a bolt handle on one side.

Since there isn't a case involved, the influence of the ejector and extractor are missing.

When the rifle is fired, the cocking piece is released and there may or may not be varying amounts of bolt thrust from the case. The bolt thrust is the chamber pressure multiplied by the area of the case ID, minus the recoil force which is the pressure on the base of the bullet multiplied by the bore area, minus the load taken by the brass. In "Rifle Accuracy Facts", Vaughn found that if a case was lubricated and had zero shoulder bump, the bolt would see the full thrust. If the case had 5 thou shoulder bump and was dry, the brass took the whole load and the bolt thrust was zero.

A lot of factory ammo has more than 5 thou shoulder bump. Even if you're a very experienced reloader, the case to case variation in shoulder bump is a larger effect than less than 100% contact. The case walls also neck down at the point they're not contacting the chamber under pressure, so the load the brass takes changes the more times they're reloaded. Shot to shot variation in pressure has an even larger effect on accuracy.

The point of that dissertation is any accuracy impacts from whatever the wipe marks suggest are buried in much larger issues.

Lapping became an every man's sort of mod decades ago, but it does more damage than good. I trued a donor R700 action a couple years ago that had been lapped by the previous owner. Whoever did the lapping must have been very patient and very stubborn. He had 100% contact, but the face at the ID of the lugs was 7 thou deeper than the OD. He ground the surface into a cone. I have no idea how much he took off in total but a PTG bolt dropped in with room to spare.

[*]Does lapping change headspace?

It's a very slow way to do it, but yes. Moves extraction timing the wrong way too.

[AreWeNotMen?]

I'm no expert, but it looks like it getting good contact on all three lugs. Why are you even looking at this?

Thanks for your initial input (that's what I was thinking), but because I wanted to look at it and I'm not an expert...sheesh! You must be an "Ignorance is Bliss" type.

[AreWeNotMen?]

The rifle is fine. but you may want to fix the loose nut behind the bolt.

Yeah, I get that alot!

[AreWeNotMen?]

Yes


Just don't.

Similar to setting up an engine, bench clearances are not running clearances. What you see there is the contact that results from the bolt under the influence of the cocking piece and cranked by a bolt handle on one side.

Since there isn't a case involved, the influence of the ejector and extractor are missing.

When the rifle is fired, the cocking piece is released and there may or may not be varying amounts of bolt thrust from the case. The bolt thrust is the chamber pressure multiplied by the area of the case ID, minus the recoil force which is the pressure on the base of the bullet multiplied by the bore area, minus the load taken by the brass. In "Rifle Accuracy Facts", Vaughn found that if a case was lubricated and had zero shoulder bump, the bolt would see the full thrust. If the case had 5 thou shoulder bump and was dry, the brass took the whole load and the bolt thrust was zero.

A lot of factory ammo has more than 5 thou shoulder bump. Even if you're a very experienced reloader, the case to case variation in shoulder bump is a larger effect than less than 100% contact. The case walls also neck down at the point they're not contacting the chamber under pressure, so the load the brass takes changes the more times they're reloaded. Shot to shot variation in pressure has an even larger effect on accuracy.

The point of that dissertation is any accuracy impacts from whatever the wipe marks suggest are buried in much larger issues.

Lapping became an every man's sort of mod decades ago, but it does more damage than good. I trued a donor R700 action a couple years ago that had been lapped by the previous owner. Whoever did the lapping must have been very patient and very stubborn. He had 100% contact, but the face at the ID of the lugs was 7 thou deeper than the OD. He ground the surface into a cone. I have no idea how much he took off in total but a PTG bolt dropped in with room to spare.


It's a very slow way to do it, but yes. Moves extraction timing the wrong way too.

Thank You - that was very instructive if not a bit above my level.

The gist I'm getting is - it's good enough, leave it alone.

[ar15barrels]

You have a Ruger RPR.
The barrel is mounted like a AR . Like a AR barrel extension.
It has a collar on it. You can not adjust the barrel headspace like a Savage rifle.
If you mess up. You would have to order a new barrel with a short throat and have to have the barrel headspaced .

False.
The RPR has a lock nut to set headspace.
Headspace is adjustable like any other barrel nut bolt action.

[baih777]

Yes


Just don't.

Similar to setting up an engine, bench clearances are not running clearances. What you see there is the contact that results from the bolt under the influence of the cocking piece and cranked by a bolt handle on one side.

Since there isn't a case involved, the influence of the ejector and extractor are missing.

When the rifle is fired, the cocking piece is released and there may or may not be varying amounts of bolt thrust from the case. The bolt thrust is the chamber pressure multiplied by the area of the case ID, minus the recoil force which is the pressure on the base of the bullet multiplied by the bore area, minus the load taken by the brass. In "Rifle Accuracy Facts", Vaughn found that if a case was lubricated and had zero shoulder bump, the bolt would see the full thrust. If the case had 5 thou shoulder bump and was dry, the brass took the whole load and the bolt thrust was zero.

A lot of factory ammo has more than 5 thou shoulder bump. Even if you're a very experienced reloader, the case to case variation in shoulder bump is a larger effect than less than 100% contact. The case walls also neck down at the point they're not contacting the chamber under pressure, so the load the brass takes changes the more times they're reloaded. Shot to shot variation in pressure has an even larger effect on accuracy.

The point of that dissertation is any accuracy impacts from whatever the wipe marks suggest are buried in much larger issues.

Lapping became an every man's sort of mod decades ago, but it does more damage than good. I trued a donor R700 action a couple years ago that had been lapped by the previous owner. Whoever did the lapping must have been very patient and very stubborn. He had 100% contact, but the face at the ID of the lugs was 7 thou deeper than the OD. He ground the surface into a cone. I have no idea how much he took off in total but a PTG bolt dropped in with room to spare.


It's a very slow way to do it, but yes. Moves extraction timing the wrong way too.

Thank you shaun for correcting me. And everybody else.
Can you recommend a action wrench to use.
I do have a gen1 and gen 2 . Gen 1 needs a new barrel.

I have been focusing on my Savage and Rem pattern (actions)

[ar15barrels]

Thank you shaun for correcting me. And everybody else.
Can you recommend a action wrench to use.
I do have a gen1 and gen 2 . Gen 1 needs a new barrel.

RPR uses a standard AR barrel nut wrench.
I recommend the Magpul AR tool as I feel its the best AR barrel nut wrench you can get for standard AR barrel nuts.

[ShaunBrady]

Can you recommend a action wrench to use.
I do have a gen1 and gen 2 . Gen 1 needs a new barrel.

I don't know if anyone makes an external action wrench for the RPR. I've seen video of schemes that try to use the slab sides in soft jaws but don't think that's a great idea. At least not for the factory barrel.

Anarchy Outdoors makes internal action wrenches for the RPRs but they shouldn't be used for removing the factory barrel. They do work well for setting up the headspace and tightening the barrel nut, but they're not completely necessary for that either. They call them Action Rods in their catalog.

https://www.anarchyoutdoors.com/action-rod-for-ruger-precision-ruger-american-rifles/

I've had good luck with a barrel vise and AR barrel nut wrench for removing factory barrels.



This is the Brownells AR15 Armorer's Wrench after being modified to work with the RPR Magnum barrel nuts. The splines are the same size but the forend retaining nut threads are a larger OD than the short action. My idea of barrel vises has become simpler over the years. I use the AR wrench as a slugging wrench and pound on it with a 3# Engineers Hammer. The oak blocks have a coat of rosin on them.

https://www.brownells.com/tools-cleaning/general-gunsmith-tools/wrenches/ar-15-armorers-wrench/#review-and-qa-block

The Brownells wrench worked without modification for the short action RPRS.
I've switched to the LRI wrenches.

https://www.longriflesinc.com/collections/gunsmithing-tools/products/lri-action-wrench-for-ruger-rpr-and-ar15s

You're probably aware that Ruger won't sell the barrel nuts to the public. One side bears against the action and the Gen 2/3 forends stop against the other face. Any peening on either side of the nut is less than ideal.