M14 Forum

Vandal

I just received a new LRB bolt, and I know I need to get a smith to check headspace and possibly lap the bolt, but could someone explain this process a bit better? What are the consequences of just dropping a new bolt in and firing it (I don't intend to do this, just looking for an explanation)? I have a TRW barrel and an LRB M14SA receiver, and I'm trying to get this thing operational as soon as I can, so I'd rather not send it off to a smith and wait months to get it back. Any home remedies?

Seventh Fleet

Will the bolt drop completely into battery and lock closed in your LRB receiver? If so the bolt lugs still needs to be checked to make sure they're both making good contact with the receiver. I take it that your barrel has been screwed into your receiver and properly indexed. If this is true that is half the battle.

You must make sure that your LRB bolt will drop fully closed into battery in your LRB receiver and that both the left and right bolt lugs have proper engagement. You can set the head space by lapping the bolt to fit your receiver but you must not lap very much metal off of either lug or you will remove the surface hardening on your bolt and ruin it.

I'm sure others will chime in with more advice. But we need to know that your barrel has already been installed and indexed in your LRB receiver and that the LRB bolt will drop fully into battery. If so is there any fore and aft slack in the bolt? If it doesn't close or just barely closes with effort, then you are in over your head and need to find a good M14 smith.

7th

Vandal

The bolt is very tight but does close in full battery on an empty chamber. When I try chambering an empty brass or dummy round it just barely doesn't go all the way down into battery. The barrel was indexed to the receiver and I just simply changed the bolt.

82nd ABN

Lapping a bolt ensures proper and even lug contact. 50% contact is acceptable as a minimum. Chances are you don't have the minimum contact. You want even lug contact to share the load, uneven loading of the lugs could cause a failure and it will more than likely cause injury. Considering you have a chrome lined barrel, the HS is set up by lapping the lugs. If you don't know what your HS is to start, you really don't have any baseline to know where to finish. What you are trying to accomplish can be done at home but the proper tools are required at a minimum a set of HS gauges. Now as far as what you are lapping, take a look at the receiver, you will notice the two lugs that mate up to the bolt lugs. These are the receiver lugs and what you will eventually need to lap the bolt into. When using a chrome lined barrel, you can but not recommended ream the chamber to fit. This is what is typically done on a short chambered barrel, one that is not chrome lined. You lap the bolt for contact and then finish ream the chamber to get the desired HS. In your case you will be lapping the bolt to get a headspace but it won't be specific. It is basically whatever you wind up with once the bolt is lapped into the receiver. If you are looking to have this work done, I would consider one of the following smiths. LRB, Shooters Den(Ted Brown) or John Wolfe, not necessarily in any order. John Is in the mid atlantic states Ted is in the pacific NW and Lrb is in the NE. Hope this helped

MemphisMachinists

If the bolt is tight on an empty chamber it probably will not close on a chambered round. If you don't have headspace guages it is kinda impossible to do it perfect.

You can make a bolt lapping tool by cutting a spent cartidge in two. Actually I used two cartridges. Put a spring inside the two halves and with the bolt stripped, work the bolt back and forth with rubbing compound on the rear of the bolt lugs were they touch the reciever. A segmented cleaning rod fits nicely into the bolt. The idea is to put some force on the bolt in a rearward direction against the reciever and mate the two surfaces against each other. The idea is simple the problem is the desired result is a precise fit. I use valve grinding compound left over from my engine rebuilding days. Can't say it is what you should do.

I'm not saying this is the right way to do this, but you asked for a home remedy version. So use a round that you know is new and fits well in another gun as your guage and just lapp it in untill it will close on that round. I assume no responsibility for it not working for you, but I have done it just this way and checked headspace later and it was well within acceptable fit. Be sure to strip the bolt! Oh by the way there is a way to do that without buying a tool if you have an empty 30-06 brass.

Try closing the bolt on a known good round. if it is not going at least a third of the way down you may have a problem.

jbrooks

Good advice above.

When you lap the boltyou also remove material from the receiver.

Don't remove more than a few thousandths from either.

If you want to fit another bolt to the receiver, and you wnat to lap that one in, you just remove even more material from the receiver.

You need headspace guages, at least a "GO"... if your bolt is tight on loaded NATO rounds, you are probably about 1.627", which is 0.003" shorter than "GO". Too tight. You should shoot for no less than about 1.632", I like even a little more. So already you will remove a total of maybe 0.005" from receiver and bolt, which is OK. Case fepth (surface hardness) is about 0.012" to 0.018" on the receiver, but don't go near that amount for removal.

Go carefully...

JWB

tokiwartooth

I think you want to put some type of articulating compound (or mark it with a perm marker) on your lug contact faces to actually see where you need to lap. You may only need to lap one lug.

82nd ABN

If you need some lapping compound let me know, I have 80 and 120 grit silicone carbide grease. You still need to have the barrel indexed so you might as well send it to a smith to have both done and fit the restof the parts yourself.

Vandal

Ok against conventional wisdom and from peer pressure, I shot the rifle today with the new bolt. I got a Sage stock and was just antsy to try it out. Anyway, factory PMC will chamber and cycled 3/4 of the time. Several times it was just too tight for the action to cycle back. It took considerable torque for me to pull the op rod back and to eject the brass. Anyway, my reloads would not chamber as I set them a little longer. Other than that, I love this Sage. Does this still match up with what you guys determined in these prior posts? Since I plan on a new barrel in the next few months, I think I'll try getting lapping compound and getting this bolt lapped. Any other insights?

82nd ABN

Wait until you get the new barrel and if you value the way your face looks don't shoot the rifle

jbrooks

Lucky dog. A little impulsive methinks...

Firing a rifle with headspace that is too tight is dangerous.

Good luck.

JWB

tonyben

You're gonna hurt yourself...

Listen to the advice.

Seventh Fleet

Wait a time with patience and do it right.

Protecting your rugged good looks, not to mention your precious vision is worth taking the time and effort to do it the smart way.

Don't shoot it again!!!

The risk is simply too great since you obviously have insufficient head space, which is more dangerous than having too much. Plus you are trying to chamber your reloads in a rifle where the bolt won't close and lock into battery.

If your safety bridge doesn't do its job correctly and prevent the rifle from firing out of battery, each and every shot and your rifle fires out of battery... You aren't going to like the consequences and neither will your very expensive rifle.

7th

MemphisMachinists

Somehow I think I have missed some of this story. I hope nothing I said or anyone else here said led you in this direction. As jbrooks said you are a lucky man. I wouldn't tempt fate twice if I were you.
You are putting your face within inches of 50,000 psi. The potential for death is here. If this thing blows up in your face and you survive you might wish you didn't.

Somebody find some links to guns that blew up. I don't have time.

tonyben

The Safety Bridge: What it is, and why it's so important...