Hmmm.. Custom 7.62X51 Barrel on a Rem 700

[usabaker]

I ordered a custom sporter barrel for a Remington 700 Short Action receiver I had; while I was at it, I had the company square the receiver, lap the lugs, and install a .250 recoil lug, I had the barrel chambered in 7.62X51 NATO with a 10:1 twist.

I know, I know, why... because I don't have one.. that's the only reason. I have a couple of 308 Win rifles already. I was a PIG Gunner in the '70s/'80s, so their is that too. But whatever, LOL, I want what I want.

I was attempting to zero the rifle with a Cabela's AG 8-32X50 Riflescope, but I couldn't get a group; the point of impact was shifting all over the place. I checked and retorqued the action screws, scope mount, and rings with no change, so I figured that I needed a better scope. After coming home, I ordered a brand new Vortex Viper HS 4-16x50 and mounted it. It was a brand new Leupold mount and Rings.

To eliminate the rifle stock as a variable, I removed the custom stock I made for the rifle, put on a Remington Factory Synthetic Stock, and mounted the new Vortex Viper HS 4-16x50.

Returning to the range, the rifles would still not group at 100 yards. The spread would be as great as 5". I have tried three different types of ammunition: Winchester White Box M80 7.62 x 51 149gn, LC M118 7.62 x 51 173gn, Match, and Malaysian L2LA 7.62x51mm NATO 146 gr FMJ, all with much the same results. All in All, I have sent less than 60 rounds down the barrel.

To eliminate the New Scope as an issue, I went home, removed the Vortex Viper HS 4-16x50, put it on a Remington 700 308Win SPS rifle, and took it back to the range. I was able to zero and group consistently with no issues.

So now the fun..

Using my Hornady Overall Length Gauge, I inserted a .308 dia pin gauge so that I could measure the distance from the end of the case mouth to the lands to get a quasi-measurement. I measured five times to get an average. I then used a Barnes 180 gn. TTSX to measure the CBTO, five times to get an average. I repeated this on my Remington SPS 308 Win to compare the results. That's where things got interesting.

The results were NOT what I expected. The Remington 700 SPS 308 Win measurements were much longer (looser?) than the 7.62X51; I had expected the opposite.

The Plug measured; 7.62X51 = 0.434" / 308WIN = 0.488" Delta Difference 0.054"

CBTO measured: 7.62X51 = 0.268" / 308WIN = 0.305" Delta Difference 0.037"


So I grabbed my 7.62X51 NATO Headspace Guages MIN 1.6355", which closed firmly tighter than I would have liked, but within specification. The bolt did not close on the 7.62X51 NATO MAX 1.6455" gauge—so Good.


Just for grins, I gauged the chamber with my 308WIN headspace gauges. The 308WIn GO gauge 1.630" closed easily, and the 308 Win No-GO gauge 1.634" closed easily. I don't have a 308WIN Field gauge 1.638" (yet), not that it would tell me much, but it would be interesting to try.


I'm not sure where I'm going to go next with this. Maybe I'll set back the shoulder on the brass I shot out of the rifle, load some rounds tailored to its chamber, and see what I get. The search goes on!

On another topic, I did buy two Ethiopian M1 Garands that I need to go through and report on.... Come soon to... after I get to the bottom of this barrel issue.

[Surpmil]

I'm not sure either, but if I'm following it sounds like your .308 WIN rifle is not correctly chambered?

BTW, when they tune up an action they true the exterior to the bolt way, the bolt to the bolt way, the boltway/exterior to the barrel threads, the front face/shoulder to the boltway/exterior, and the face of the bolt to all of them?

I ask because you didn't mention the bolt face.

[Sapper740]

Try ZQI or IMI 7.62 NATO ammunition, you might find they supply better accuracy. After I bought my Ishy 2A I wanted to find a factory load that was reasonably accurate as the last thing I have time for is working up yet another handload. I'm still working on all the permutations for my Territorial rifle that I bought last year. I shot Igman, LC, ZQI and IMI offerings and was pleasantly surprised at how accurate the ZQI was....even better than the Israeli ammo.

[tiriaq]

Throw most any .308/7.62 barrel on a stock, untuned 700 action, and it will do better than 5" at a 100.
If you want to tighten up the headspace, just turn a few thou off the shoulder, barrel face and counterbore face, essentially screwing the barrel in a bit. But I doubt that is going to fix the problem. It would improve the handloading situation.
I suspect the fundamental issue is with the barrel - most any barrel will do better than that.