I’ve seen some people before talk about truing up the front of the receiver extension to make a perfectly level and squared up contact between the barrel extension and the receiver as a method to really tighten up the accuracy of the gun.
I never thought much about it because I wasn’t interested in squeezing every last bit of accuracy out of my guns…yet.
I’ve come across a few companies that now do it as a service package for accurizing an AR.
Do you think there is merit to this process? Would there be any appreciable gain? Or is this all just pixie dust and unicorn jizz?
The gun I have in mind is a precision .308 project that is currently at a stand still due to the panic, but will ultimately turn into a no-expenses-spared kind of thing (well…not literally…I’m not that rich).
Best bet would be to just buy one that’s true in the first place. Something like the Rainier Arms Ultramatch or Vltor MUR will be machined precisely and ensure everything is lines up straight. I’m not sure what truing could be performed on an AR upper after it’s machined but I can’t imagine it would exceed what high end manufacturers are accomplishing with strict QC and CNC machines. Besides that I think the main thing that matters is having the flat top perfectly in line with the bore/receiver face and built as much rigidity into the design as possible. I’d also wantthe barrel extension to have minimum clearance in the receiver i.e. a slip fit.
I would be all over that Rainier receiver if they made it in .308 (I’m already using the Ultramatch .308 barrel, though).
There doesn’t seem to be a whole lot of options out there regarding .308 upper receivers like there are with the smaller AR-15 platform. I have seen 'smiths polish the mating surface, which is why I’m asking.
I’m just wondering if anyone thinks its actually worth the expense.
I wish I could quote a source but I believe this it total BS! Even if a bolt action rifle receiver is trued it will gain nothing if the barrel used is not cut to the same standards.
I tend to agree w/ posts above regarding in-spec / out-o-spec. Of course it’s true regarding barrel etc.
I always check specs for QC. If you examine the interface where receiver links up with barrel nut or rail interface on an OBR / LMT / KAC / Barrett (which are all sub MOA capable) you’ll notice how each manufacture addresses (w/ their proprietary methods, patents etc.) this important accuracy issue.
A Bullet (missile) doesn’t give a Rat’s Ass which breech & tube it’s launched from.
I also agree about .308 L/R availability & know what you are referring to. While DPMS seems to be the prevailing pattern there are non-compatability issues w/ certain components. Proprietary specs are respected for the most part.
FWIW, I’ve been working w/ Seekins & SI Defense stuff lately that is pretty dead nuts on typically. NEMO Arms has some good stuff I’ve been working with that might be worth a look at.
I know Young’s MFG. .308 BCG’s production are already spoken for so that’s going to be like finding Unicorn Jizz for sure.
I did contact a company local to me who performs this service on AR-15s and asked about doing it on a .308. They said it can be done, but there would be an extra cost to set up for it since they don’t currently have the tools.
That said, I don’t think there will be a need for it. I’d rather get the gun assembled and shooting to see where I’m at. If I feel like there is room to squeeze more out of it, and there aren’t any other things that can be done, then I’ll consider doing this. From what I’ve read about the manufacturer of the upper receiver, I don’t suspect there will be any issues with the spec. I’m probably not a good enough shooter at this point anyway to really notice a difference.
Voodoo, I was planning on getting a Young MFG whenever I can find one. Who is sucking them up?
The outfit I work at regularly does stuff at ~.0002" precision, but frankly no projectile is going to give half a crap about that - it’s like trying to figure out how much better a lighter kid’s see-saw will do at flinging things when there’s an elephant at the other end, it’s going to be completely lost in that process.
This does have me thinking about how reasonable it would be to start making the .308 uppers though…
While i think the discussion is interesting, I don’t think it matters (enough). For me, if you want improved accuracy, fit the bolt to the barrel, use the lowest ACCEPTABLE torque value on the barrel nut and use spacers to time the flash suppressor/MB.
Wait lowest torque? I’m no sniper, but it seems whenever these sort of topics come up (generall talking bolt guns) I’ve always seen higher torque numbers. Can you explain/help me understand here?
If we are talking about the barrel nut, it depends. For instance, if the rail system has an anti-rotational system (like the Noveske NSR MUR and Rail), I might be in the 40ft LBS range.
If we are talking about FH/MB’s, I like to keep these as light as possible. For instance, if you are mounting an A2 birdcage with a crush washer and it is all the way around the other side, that is just too much torque IMHO. I will shim it so that I only need to go about 1/4-1/2 an inch before it is lined up.
My feeling is anything that will keep the bolt and barrel as aligned as possible cannot hurt. I have had more than a few uppers built and all have been squared or at least checked. Most have needed virtually no cutting. Others took some but not excessive IMHO.
If I were you I would just find a good quality upper and barrel and not worry about this. I also have an SI Defense 308 upper/lower and am very happy with the finish quality and fitment. As for barrels, why not save the $$$ from this arguably unnecessary step and spend the $$$ on a nice Shilen or Krieger blank?
In my experience where I’ve done it and it may work for better consistent accuracy maybe 50% of the time.
FWIW the most accurate AR upper I’ve ever assembled shot a 0.26" 5 shot @ 100yd group when new. On that upper I didn’t lap/true the upper receiver.
Where using the tool to make a difference is when installing LaRue or Noveske NSR rails and you need that .003" more rotation for proper alignment of the rail to the receiver under while staying under 80ft lbs of bbl nut torque.
Then that is a whole different ball of wax as opposed to the OP’s question.
Material removal from the receiver for timing is not the same as simply squaring the receiver end.
I wouldn’t expect truing the face to effect the accuracy of the rifle at all. Just that the optics and bore will be in better alignment. This isn’t so much an accuracy, as to group size, as people are thinking about.
I think there is merit to the process, but IMO you are better off with a better solution up front. Who is to say after truing the face that the top rail is even in alignment with the bore?
I would rather have a tight fit to the barrel extension, and that’s second to headspace. If you’re on the large end of headspace you won’t see good groups unless you are shoulder bumping once fired from that particular rifle.
I agree with Grant, that in the order of priority when building an upper, truing is pretty low.
Truing the front of the receiver where it contacts the barrel nut is only one small part of the equation. The barrel nut, receiver extension, locking lugs on the receiver extension and bolt… would all have to be trued. That is if you are going to do this like a precision bolt gun.
ETA: In my opinion the your gain, if any, would be so insignificant that it is not worth it. As someone else pointed out it does have a use in clocking/indexing barrel nuts of some rail systems.
My two cents is: squaring may not help, but it can’t hurt unless you over do it.
My two free floated scoped hunting uppers are squared.
My two handguarded iron sighted fighting uppers are stock BCM builds.
If you remove too much material from the receiver, the barrel sits too deep into the receiver and the feed ramps on the extension can form a catch point.
IMO, the transition from the upper receiver feed ramps to the barrel extension feed ramps should have a very slight waterfall or shingle between them.
