New AR build for PRS, ammo question.

[3-0-hate]

I put together a fairly budget AR for PRS, just to see how good something could be on a shoestring budget. Well, I got it put together and the thing shoots quite well, given the fact that it has a GI trigger that I stoned and polished myself, and an AR stoner barrel (20" 5R stainless/fluted). The one place I didn't skimp that much on was glass, it has a Bushnell FFP LRS 6-24x50 mounted on it, albeit in a cheap mount (that has at least been lapped).

The main question I have is that I always seem to chase real tiny SD numbers in my bolt guns, and usually end up around 3fps or so because I know its going to reduce my vertical dispersion at distance. The club matches that I shoot up here has a few shots that reach out to around 910 yards, pretty consistently. In order to get out there before going trans sonic, I need to push the Hornady 75gr bullets at around 2900fps. In fact 2875fps keeps me supersonic to around 920, and at that velocity, Im getting an SD of 7.8, which Im ok with in this gun. If I push it to 2930fps (26gr Varget) I stay supersonic to 940yards, which would give me a little more wiggle room if they push the targets back a bit, BUT, my SD climbs to 13fps. Am I just being pedantic right now or should I download to the 2875fps and keep the better SD? Both loads hammer at 200 yards btw.

Photo for attention

 

[SporterII]

26 gr. Of varget is a packed case full in 223. Hard on an AR possibly? 2850+ in 20" with 25gr.? Personally I would stop and see if you get away with that this summer. Even if it means a couple points dropped. It's good speed on 20".

 

[djarecke]

Take a look at your wind call at 2750, 2800, and 2850 FPS. I seriously doubt it's more than 1/10th of a MIL.

26 grains of Varget is way too much powder behind a 75 grain bullet, and 2900 FPS out of a 20" barrel is just not realistic. You honestly don't need to drive it that hard to make good hits.

Not to nit-pick, but 3FPS is inside the error allowance for any chronograph I've ever seen. A $400 or $500 system just isn't that accurate. I wouldn't obsess about the numbers and get more time behind the rifle learning to read wind and mirage.

Great looking rifle by the way!

 

[3-0-hate]

Thanks guys. All measurements were taken by a magneto speed V3.

26gr Varget

25.7gr Varget

 

[redneckbmxer24]

Dude you’re going to have pressure issues, 26gr of Varget is way hot behind a 75gr bullet. I’d back down well below 25gr unless you want to risk blowing primers or locking your gun up at a match. There’s usually a very solid node 24.0-24.5gr with Varget and 75-77gr bullets.

There’s powders that can safely push a 75gr bullet to those velocities from a 20” barrel but Varget isn’t it. I personally run Varget however because to me the consistency I get with it is worth more than more velocity with other powders I’ve tried.

8208 is a great powder for velocity but you’re not going to get the ES/SD that you can get with Varget.

 

[Mordamer]

Back down in velocity. You do not need to stay supersonic to make hits. I'd say that 2,800 FPS is good velocity for your setup. I can't believe you are using 26 grains of Varget without already seeing pressure signs.

I'd also add that I think you have a cool idea shooting a rig like that in matches. I believe you can do quite well and I bet it would be a ton of fun to shoot a 5.56 gas gun in a match. Makes me wonder how fast I could run the PRS skills stage 1 with that setup.

 

[3-0-hate]

I hear what you guys are saying about backing down, but the pressure just isn't there unless Im seriously missing something here. Two of these cases are the 26gr load, and one is 25gr. Its obvious from the flatter primers, but there is no cratering that I can feel with my fingernail and the case head looks almost perfect, as do the rims. There is some slight imprints from the ejector, but nothing that I would call excessive.

I may back down to the 25.7gr charge to give me some safety margin. I know its still above book, but unless someone can see something I cant, I may try to play with it.

 

[spife7980]

There is some slight imprints from the ejector, but nothing that I would call excessive.

If you are seeing ejectors prints then you are already over pressure. If you were in safe pressures you wouldnt see any.

 

[redneckbmxer24]

You’re getting ejector marks with Lapua brass which is ultra tough... yeah you’re over pressure.

 

[Mordamer]

I hear what you guys are saying about backing down, but the pressure just isn't there unless Im seriously missing something here. Two of these cases are the 26gr load, and one is 25gr. Its obvious from the flatter primers, but there is no cratering that I can feel with my fingernail and the case head looks almost perfect, as do the rims. There is some slight imprints from the ejector, but nothing that I would call excessive.

I may back down to the 25.7gr charge to give me some safety margin. I know its still above book, but unless someone can see something I cant, I may try to play with it.

They look fine to me. Shoot it and have fun.

 

[USMC 308]

 

[Shawn1492]

I’m just about to get that barrel myself for the same reason. When you say it hammers at 200 what size groups are you getting?

 

[3-0-hate]

I’m just about to get that barrel myself for the same reason. When you say it hammers at 200 what size groups are you getting?

It hovers right around 1/2-3/4 moa. Totally sufficient given the cost/performance equation. My KWhite Oak Krieger barrel does a little bit better, but it's marginally for how much more it costs.

Some of the reports have been hit or miss on these though. I hand lapped mine when I got it and I think that helped a bit.