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Problems trying to get a Rock River to group

I have a Rock River Predator Rursuit 20" that I have been trying to get to group with little success. I have a 12-42 Nightforce BR scope that I transfered from another rifle mounted on it and I know the scope is good and everything is tight.

The barrel is a 1 in 8 and I originally tried 50gr v-max with Benchmark because I have an abundance of both. I wasn't getting consistant groups so I thought the bullets might have been to light to stabilize. I tried a ladder test with 55gr v max and Benchmark and found a load that shot some decent groups averaging 1/2"-3/4" at 100 yards.

Last night I tried that same load at 425 yards and was shooting at a 12" steel plate. I knew what the hold should be which I confirmed with a ballistic calculator. I had a lot of vertical stringing that wasn't showing up at the close range, I even had rounds going under and over the plate.

I am using LC brass that I trimmed but has multiple year headstamps and I am wondering if that could be part of the problem. I am using Federal 205M primers and I have standard CCI small rifle primers I can try also. I am looking for advice on what I should try next and any help would be appreciated. I wouldn't think 55gr bullets would be too light to stabilize in a 8 twist but maybe I need to try heavier bullets also.
 
I would run some of those loads over a chronograph, and weigh the brass to see if it has much weight variation, by year.
 
I had the same RRA PP, 1/8" twist, 20" bbl and it shot my 50g vmax in front of 27g W748, cci400 or WSRP into nice small groups at 100-200 yds. No problem smacking steel at 400-600yds with that load w/dialing up or holding w/mil dots.
COL was 2.250" just shy of OL mag length. The 55g vmax was as small w/27g w748 same col & primers.
My scope was a Nikon buckmaster 6-18x40 in a PEPR 1pc mount.
My chrony averaged 3348 fps w/the 50g load.
My brass was as mixed as cookie dough, win/LC/rp/IMI/FC/pmc/Pvi......it did not matter, they all shot the same.
I took out the 2 stage & dropped in a 3lb timney, but no matter it shot those loads small.
 
BobLeeSwagger223 said:
I have a Rock River Predator Rursuit 20" that I have been trying to get to group with little success. I have a 12-42 Nightforce BR scope that I transfered from another rifle mounted on it and I know the scope is good and everything is tight.

The barrel is a 1 in 8 and I originally tried 50gr v-max with Benchmark because I have an abundance of both. I wasn't getting consistant groups so I thought the bullets might have been to light to stabilize. I tried a ladder test with 55gr v max and Benchmark and found a load that shot some decent groups averaging 1/2"-3/4" at 100 yards.

Last night I tried that same load at 425 yards and was shooting at a 12" steel plate. I knew what the hold should be which I confirmed with a ballistic calculator. I had a lot of vertical stringing that wasn't showing up at the close range, I even had rounds going under and over the plate.

I am using LC brass that I trimmed but has multiple year headstamps and I am wondering if that could be part of the problem. I am using Federal 205M primers and I have standard CCI small rifle primers I can try also. I am looking for advice on what I should try next and any help would be appreciated. I wouldn't think 55gr bullets would be too light to stabilize in a 8 twist but maybe I need to try heavier bullets also.

I'm not sure you understand the concept of stability with respect to bullets and rifles. A 1:8 twist in a .223 will stabilize all bullet weights except for the 90 grainers. Using lighter (shorter) bullets in a 1:8 does not cause them to lose stability, au contraire they will be even more stabilized.

Now for your issue, pushing 55gr V-max to 400+ yards and getting elevation issues. I don't think the different years headstamps are the issue. You did not tell us how you measure the powder. I'm going on the premise that you are a reasonably competent shooter, nobody messed with the bullets before loading and the conditions were mild. So to me that leaves variations in the powder charge as a probable cause for elevation issues. Tell us more about your loading technique and then, yes, let's chrono these puppies.
 
Thanks for all the replies!

I am using a RCBS Chargemaster to weigh each charge and use a standard Redding seating die and I FL size each case. I use a Rockchucker press and the RCBS trimpro with 3 way cutter to trim cases.

I have a 223 bolt rifle that has shot several 1/4" 5 shot groups with Benchmark and 50gr vmax so I have great confidence in that combo but I am wondering if I need to be trying different powders. I have RL15 and Hornady 75gr BTHP bullets so I might try those next. Sadly I don't have a chrono, I have just always let the targets tell me how much powder to use. It would be handy to see what my SD is. Maybe I will need to think about investing in one.
 
I disagree with the statement that a 1/8 will stabilize all bullet weights except for the 90's. I have a RRA with a Kreiger 1/8 (service rifle upper ) and it will not stabilize the long hornady 80 Amax's. In general you are correct but some combinations of bullet type, velocity, air density, etc will provide only marginal stability.
 
if you can find them, try some berger 70 vlds and some 4895 or varget. that will reach out there real nice for you and you can get some good velocity with them. I am partial to wolf primers as well, as my consistency is much better since I switched over.
 
BobLeeSwagger223 said:
Thanks for all the replies!

I am using a RCBS Chargemaster to weigh each charge and use a standard Redding seating die and I FL size each case. I use a Rockchucker press and the RCBS trimpro with 3 way cutter to trim cases.

I have a 223 bolt rifle that has shot several 1/4" 5 shot groups with Benchmark and 50gr vmax so I have great confidence in that combo but I am wondering if I need to be trying different powders. I have RL15 and Hornady 75gr BTHP bullets so I might try those next. Sadly I don't have a chrono, I have just always let the targets tell me how much powder to use. It would be handy to see what my SD is. Maybe I will need to think about investing in one.

Ok. I don't think it's you powder charge unless something is wrong with the Chargemaster. I will go on the premise that it is working fine and that you know how to use it properly.

It could be one heck of a coincidence, but the description of you problem reminds me of a similar occurrence on another thread just recently. You might want to read this thread, look at my explanations and the final observations, then come back here and we can discuss further.

http://forum.accurateshooter.com/index.php?topic=3813664.0

I'm not saying that's your issue for certain, but the similarities are just too striking and I have further thoughts on your issue.
 
I have been thinking this over all day. I think my next step is to try the exact same load with CCI standard small rifle primers and see how it groups.

I also just cracked a new 8lb container of Benchmark when I got this rifle so I am thinking I should try a different lot of powder.

Since I have only shot a few really good groups with this combo and it seems like I haven't been getting any consistant results I might try a completely different powder and see what happens.

Do those sound like good ideas? What would be a good powder to try for 50-55gr bullets in an AR?
 
I gotta chime in too. I also have the very same rifle as you do. I load midsouth shooters supply varmint nightmare extreme 55 gr. flat base hollow points. these are cheap but very accurate in my rifle. I keep them at 3150 fps. I use H-335 ball powder and std cci or win small rifle primers. I use a RCBS uniflow powder dumper with 24.7 gr. of this H-335. I F/L size all my brass. the inside of every case is sterile. no contaminants of any kind. if your bullets are stringing vertical at 200, 300 and 400 I would suspect powder, powder charge, maybe even a barrel obstruction.(copper build up)? what do your spent primers look like. is there any radius left on the edge of the primer?> or is it flat like a sheet of glass?
 
Triggerhappy- sorry I forgot to mention barrel cleaning. The barrel cleans up great and I have tried a completely clean copper free barrel as well as fouled with no noticeable difference either way. Primers look good. Just dimpled like any shot in my bolt rifles. I'm not getting any pressure signs either.

I am going to try the same load with CCI standard primers and then if that doesn't fix it I will try a new powder. Thanks a ton for all the help. I really thought finding a load with this rifle would be more easy.
 
I see that you completely ignored my previous post and that's certainly your right to do so.

I will try to explain my complete thinking one last time and then leave you alone.

I believe that you do not have a "load or component" problem per se, what you have is a bullet damage problem. You are using thin-skinned varmint bullets in a fast twisted rifle with a long barrel.

You mentioned that your load is grouping 1/2 to 3/4 inch at 100 yards. Unless you are a totally incompetent trigger puller you should expect group around 3-4 inches at 400 yards, properly under 6 inches and you certainly should have no problems consistently hitting a 12 inch steel plate. That's if everything worked as expected.

Because you are getting vertical stringing I believe your bullets are suffering from dynamic instability induced by the fast twist, high velocity and very thin jacket of the V-Max. You do not see the problem at 100 yards because it takes time (distance) for dynamic instability to affect the flight of the bullet. One of things it will do is mess with the BC of the bullet in unpredictable ways, which will cause vertical stringing and it may also affect horizontal and anything in between.

My belief is that your bullets are ever so slightly damaged by the fast twist that some of them are affected by dynamic instability. Some are not or are affected to a lesser extent.

You say that you load works fine in a bolt rifle of the same caliber, I will say that there is a great chance that bolt rifle has a 1:12 twist, which is much more appropriate for these thin-skinned bullets. A 16 inch barrel will not generate as much RPM as the 20 inch and so the dynamic instability will not be as great and may never even be observed.

My suggestion is to try a more solid 52 or 55 grain bullet in your 1:8 twist, I've had great success with the Sierra MK offerings in my 1:8 twisted rifles; their jackets are thick. Another excellent suggestion was made earlier (and simply dismissed) to use heavier bullets. In fact the 1:8 twist was designed for heavier, longer bullets. If you insist on using the thin-skinned V-max bullets, reduce the powder charge.

Good luck.
 
I run the hornady 68 grain match bullets and no matter the powder,they seem to fly pretty good.I have killed flys at 100 yds many times with groups in the high .2's.I use h335 and blc-2 which I have lots of with great results.I know bergers are probably better but the 68's work great and forget the v-max unless your hunting ground hogs . But if you want better accuaracy try a match bullet like bayou shooter suggested.By the way these match bullets do a good job on ground hogs and other vermin.By the way if you want even more consistent accuracy dump the wilson barrel on your rifle and get an aftermarket barrel such as kreiger or whatever.
 
My guess is that you are shooting off a bipod and it is hopping.

Shoot it with a tight sling from prone with sandbags under your forward hand and let us know how it shoots.

ETA: What about wind? Even a headwind or a tailwind can affect elevation, especially if it hits something and bumps up or rolls over onto itself. This thread reminded me: forum.accurateshooter.com/index.php?topic=3815252
 
I just got the same weapon, loading up a variety of bullets/ powders to test. I notice that the 75 & 77's require very deep seating to function in a Mag. I'm wondering if a Lee crimp die or an RCBS taper crimp die may be required ??
 
BobLeeSwagger223 said:
I am using LC brass that I trimmed but has multiple year headstamps and I am wondering if that could be part of the problem.

The year of manufacture of LC brass is not like a lot number - there is nothing about 2005 cases that are different than 2006... so there is no point to sorting by date.

There IS a point to sorting by weight and condition, and maybe neck thickness and run-out.
 
Thanks for all the replies!

bayou shooter: sorry if you feel I ignored your post, it was not my intention. I am just limited with what I have on hand and there are no reloading supplies to be found around here so I am running on what I stocked up with before this panic buying started. I did have 21 bullets left of Hornady 75gr hpbt that I have loaded with RL15 to try. I am going to try some Matchkings also when I am able to find some.

In the Sierra loading manual they listed RL7 as the most accurate load with 55gr bullets in an AR so I loaded some of those to try as well.

Lastly I tried the same load I was using and substituted standard CCI SR primers for the 205m to see if that matters at all.

For a rest I am using a Caldwell fully adjustable pedistal type rest with a rear bag. I am used to this setup with my other rifles so I am trying to use it with the RRA.

On the last day I was out the wind was from 5-8mph with a direct crosswind. Which wouldn't have effected the vertical stringing. I will be going out again this week on a day with good conditions. I like winds close to 5mph or less for load testing.
 
Yesterday was perfect conditions with a 5mph wind on a sunny day. I allowed plenty of time for the barrel to cool between 5 shot 100 yard groups and sadly there weren't any groups worth bragging about.

Changing primers from 205 to CCI standard small rifle in the 55 v-max/Benchmark load didn't change a thing. The group was virtually identical.

The 75 bthp/ RL15 load might be somewhat promising. I only had 21 bullets left to try and the groups were close to 3/4" give or take. They weren't really consistant but one of the groups was close to 1/2".

The RL7 / 55 vmax combo shot the best. Consistency seemed very good and several groups were 1/2". The disappointing part of the story is they were listed as a max load in the Sierra manual but they wouldn't function in the rifle. I had 3 malfunctions in 20 rounds, they seemed weak compared the the other loads and was struggling to push the bolt all the way back.

I did some serious thinking and have decided that I am trying to get a Rock River to shoot groups like my Cooper and the rest of my bolt rifles. I have decided it might be time to part ways and I should end up close to a wash because the market is so good on those rifles right now and resale is good.

Thanks so much for all the help with this rifle. I am going to stick to bolt rifles for serious accuracy work.
 

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