Service Rifle question

[XTR]

Is there an adjustable gas block front sight for an AR-15 that is legal to use in Service Rifle?

 

[watercam]

Good question, someone will no doubt answer it shortly. The point is though, does one really need it? I was under the impression that the adjustable gas blocks for ARs (what I assume we are talking about) had more to do with whether or not one was using a suppressor or not. As those are not legal, a straight block should be all you need (in Service Rifle as opposed to Match rifle with an AR platform). M1As are a different kettle of fish but folks have been shooting them in competition for decades in Military stock configuration. For both it is a matter of finding loads that do what you need for all four ranges one shoots in High Power (if one includes 500 yds.).

 

[spclark]

Not that I know of, no. All those I've seen or heard of don't incorporate the front sight mount, being intended for use on match rifles. I had one on a 6.5 Grendel upper ten years ago & took it off it worked so poorly.

Why would you even want one on a service rifle if you expect to use it in sanctioned competition? Accurate, consistent loads aren't that hot & at this point pretty well established; pick a load others use & go shoot rather than mess with load testing trying to 're-invent the wheel.'

 

[jameydan]

I would expect that an adjustable gas block would be legal on an M110 as those rules run a little less stringent compared to the AR15/M16 Service rifles.

JP does make an A2 front sight tower/adjustable gas block. But, I would seek specific approval on that item as it is a little different looking than the standard A2 front sight tower/gas block. http://www.jprifles.com/1.4.6_gs.php (my humble opinion is that they would not pass..)

Adjustable gas blocks can serve a few purposes on a service rifle - they can deal with an oversized gas port in the barrel and they can also be put to use for taming extraction especially when using warm loads, slow powder and heavy bullets (as in shooting LR service rifle).

Another option is the adjustable gas keys for the bolt carrier from Sun Devil and Rubber City Armory which supposedly serve the same/similar purpose. I have not used one and can not comment on their capability.

 

[XTR]

That is kind of what I was thinking. Wonder if the JP is legal?

Running 80s at warm loads cycles the bolt pretty hard. I've added a heavier weight but I was just thinking that an adjustable port would really be useful to make the extraction more civilized.

 

[rminut]

would you be willing to post the details of the load used? in service rifle the point of penny wise, pound foolish comes much earlier than in other disciplines.

 

[akajun]

Why is everyone concerned with over gassing on an ar? That's what the buffer is for? Plus the buffer smacks the back of the buffer tube, both cheap and easily replaceable parts.

 

[Heman]

No an adjustable gas block is not legal for service rifle. There are some out there, but they are not legal. First year I shot Perry on palma day I was squaded with an AMU shooter who was shooting M16, was shooting nuclear loads but had standard gas system. To help your issues if you run a Carrier weight system that will help with the pressure issues. We (brother and I) run those in our service rifles and handles our 80gr loads (25.2gr of Varget and either a 80gr VLD or AMax) just fine out of a 1:7 (his) or 1:8 (mine).

 

[chkunz]

Why is everyone concerned with over gassing on an ar? That's what the buffer is for? Plus the buffer smacks the back of the buffer tube, both cheap and easily replaceable parts.

sometimes they will not function properly if you get out of a narrow range of port pressure.

 

[akajun]

Why is everyone concerned with over gassing on an ar? That's what the buffer is for? Plus the buffer smacks the back of the buffer tube, both cheap and easily replaceable parts.

sometimes they will not function properly if you get out of a narrow range of port pressure.

If you have function problems with an ar, I can guarantee the fact the gas port may be a few thousandths over is not your problem, you have other issues.
This whole issue of " bolt bounce" is not s valid theory .
Undergassed, yes, overgassed I've never seen cause a problem.
I do however still the gas ports on my service and match rifles just big enough to get reliable cycling though,

 

[XTR]

would you be willing to post the details of the load used? in service rifle the point of penny wise, pound foolish comes much earlier than in other disciplines.

I was ignoring this but based on our earlier conversation I'll answer you.

ORSA had a number of mid range matches throughout the year. I'm already shooting HM in midrange F-TR (not that much of an accomplishment really in F class mid range) and we really don't get a lot of turnout in F-TR for some of these matches so I was considering bringing my service rifle out for some of the 600yd HP matches and as a part of that thought I was considering running the throat out a bit on an upper and running 90s.

I've invested a lot of time and components into getting 90s to run in a long barreled bolt gun, but have not experimented with them in the AR. All my AR loads to date are 77s and 80s, but it seemed to be something I might like to try.


I don't pretend to be particularly well versed in the ways of the AR but I have read enough to understand that high port pressures running heavies hot can result in some pretty hard bolt cycling. (kind of makes sense?) thus the question in the original post. I don't want to make any changes to my White Oak upper that will make it not correct for Service Rifle competition.

 

[rminut]

I watched all those 90gr and MR2000 discussions. I often thought-people why all the focus on 90's? it's just 600, shoot 80's. the winds calls might not be that far off from a slow 80gr at 600 to a fast 210gr at 1k. plus it's cheaper, that's just me being pragmatic. I shoot nothing but Nosler 155's at 600 and 800, cheap and makes me watch the wind better. no excuse but if i drop points, oh well it's only 600 anyways.

more to the point, I only know one person shooting 90's in a service rifle. it works for him and last he told me he used VV-135!! of all things. so maybe slow powder isn't needed. most use yellow or red box 80's. some even use 75VLD going FAST.

 

[Caliche Pit]

Ditto on the Tubb carrier weight system as Heman stated. I have shot a ton of 90 grainers over the years, and my advice would be stick with the Berger 80 VLD running warm and you will be a happy camper at 600. Brass will last much longer than if you are pushing 90's.

 

[XTR]

If I don't bother with the 90s, and I may not, I've got a couple of thousand Nosler 80s I can use. I'm going to suck at it, I know that. I've been in a sling half a dozen times, ever, and some of those were a long time ago.

As for the 90s and 2000MR, I gave up on that powder, in all applications except hunting, and actually on that rifle. I'll get a good load for it and sell it for a good price to someone. I decided I don't need another (third) F-TR rifle in the safe. I just got a 223 barrel and PT&G bolt for my backup rifle and worked up a load.

 

[rminut]

I never tried the 90's because of all the headaches I saw guys posting about. my friend does a lot of testing and brass work for his. he likes that sort of stuff, plus he is still chasing leg points, so he sees the worth in it.

I became amazed by some of the top shooters in Phoenix. They shoot 80's and just read the wind like there is no tomorrow. One is on the Palma team for the second time and the other was trying for a coaching spot. They don't worry about giving up a little horsepower, they just focus on the wind and are always near or at the top of the list. Both of them have won the Creedmore Cup using a .223.

MR2000 should work just fine in service rifle by the way. don't go crazy trying to push the velocity though, then it will hammer the carrier back even with an 80gr.

 

[XTR]

Without going into a lot of details I can tell you, that at least in a 308, with the accuracy required for F-TR, 2000MR is just not consistent enough. In a SR it may do fine, but there are a bunch of us shooting F-TR who have been down that road and back, and unfortunately I didn't meet them all until I got back, or until we all started swapping stories.

 

[akajun]

Ditch the 90's for a service rifle , you just can't get them going fast enough to take advantage of the 90 in a 20" barrel. If you want to try something other than 80s , try berger 80.5 or 82's. They shoot great in service rifles, or anything 1/8 twist or faster, and have a better bc than 80's, and are Jump tolerant, though I load mine at .015 from the lands .
I switched from 80's after shooting a team match at Perry where my teammates were .5 minutes less on windage with them than I was with 80's.
I shoot mine with 24.3gr of reloader 15 , but have also developed a load for our juniors with 24.2 of varget and 23.3 of 8208.

 

[XTR]

I've got a bunch of 80s loaded up over AA2230. I picked the ball powder so it would meter well on my Dillon. I'm not sure what the load was/is with out going back and looking. It worked OK from the short lines. Never tried it at 600.