39 grain BK problems?

TaterTot

TaterTot

New member
Not real sure what happened yesterday. I loaded up some 39 grain BlitzKings for my 20 Practical AR over IMR 8208. I shot the first round of charges at 25 grains and ended up with the following group:



I had subsequent charges loaded at 25.2, 25.4, and so on in .2 grain increments. The groups from the next three charges all looked more like a pattern of 00 buck shot. I'm talking 4" + sized groups.

My barrel is supposed to be an 11 twist, but I haven't checked it yet to verify that. I do have a load with 35 grain Bergers that shot really well, but I didn't have them with me at the time to see if they still grouped like they should. I might be able to shoot a quick group with them tomorrow.

I'm thinking maybe a scope issue, but if it's not the scope, is there something else on the rifle that I should look into? I did check the rings and scope mount while I was at the range. Everything was tight.

Any suggestions?
 
To go from that, to 4+", all at once, something has to have crapped the bed and it shouldn't be too hard to track down where the smell is coming from.

Scopes are snakes and always suspect #1. After that, I don't know diddly about AR's so wouldn't know where to start. On a bolt gun, there just isn't much besides a scope failure that can cause a sudden huge change like that though.

- DAA
 
Originally Posted By: DAATo go from that, to 4+", all at once, something has to have crapped the bed and it shouldn't be too hard to track down where the smell is coming from.

Scopes are snakes and always suspect #1. After that, I don't know diddly about AR's so wouldn't know where to start. On a bolt gun, there just isn't much besides a scope failure that can cause a sudden huge change like that though.

- DAA

I hope to be able to check the scope tomorrow. I can't think of anything with the rifle that would suddenly cause the issue. All rounds cycled properly, no pressure signs, nothing attached to or touching the barrel, and nothing different with the rounds other than charge weight.

I'm hoping it's an optics issue, even though I've only used it to fire less than 100 rounds.
 
An 11 twist should handle the 39gr with little problem....Question one, How clean is your barrel?? Those light/thin skinned bullets can be thrown off with caked powder residue...I had that problem and thought my barrel was clean until I had it bore scoped and was informed that I had about eight inches of caked burned powder from the chamber forward....Took a lot of cleaning to get it out...

I've always built my test loads in .1gr increments due to the small case and bullet size...doing it at .2gr, you may be going on either side of the magic accuracy group...

When I get a good three shot group, I fire the other two for verification...If I'm not getting the group that I like, I break down the remaining two and save them for rebuilding the good one(s)...Statistically, my really good groupings usually show up from .4-.7gr below published max loads from a commercial source..The .20 calibers can be really picky about your charge weights....

The 39gr SBK in a .204 usually shoots best with a longer jump to the lands than the .223, hopefully you are not trying to keep close tolerances on your overall length in that respect...
 
Old Turtle,
I don't have access to a bore scope, but my barrel is relatively clean. I patched it with Butch's Bore Shine until the patches come through clean. That was at about the 60 round count. I believe I am just under 100 rounds down the tube right now, including the 17 rounds I fired while testing these 39 grain bullets.

I did check the barrel with a cleaning rod and tight fitting patch. I checked it 5 times and it appears to be as close to an 11 twist as I can measure with this "scientific" method.

If everything checks out with my previously known good load, I may retest with increments of .1 grain. I did load these up with a .015 jump to the lands, which gives them an average of 2.214 OAL. My 20 Practical barrel has a relatively short throat.
 
I went and double checked everything on my rifle as far a scope mounting. I started by checking to see if everything was leveled. I used multiple Wheeler levels on the barrel, lower receiver, and the elevation turret. I noticed a slight cant to the reticle. I do have to say that I didn't get as technical when I originally mounted the scope.



I hung this target at about 25 yards and made sure it was level. Then I went back and leveled my rifle. This is the view I had. The crosshairs appear to be slightly canted counter-clockwise. (Might be hard to see with my cell phone pic)

The scope in question is a Vortex Viper HS-T 4-16x44. It was purchased brand new and has only been used on this rifle. Not sure if this means anything as far as my odd grouping issues.
 
Not familiar with the 20 Practical, but have put LOTS of rounds thru two Cooper .204's. One of my guns did worse than yours, turned out to be copper build up in the bbl. I can't get 60 rounds thru my Coopers without cleaning, more like 30. When shooting prairie dogs, my average is 25-30 rounds and need cleaning. Cooper advised they use Wipe Out even on the really dirty bbl's, so that's what I've switched to, sometimes using a nylon brush with it. I've quit using the metal brushes altogether. Keep us posted on what you find out.
 
Most gun smiths have a bore scope and if you have one close to you, it would be worth having them take a look...My wife bought me one for Christmas a couple of years ago....I look at the cost of one just like some look at having a gun safe...If I'm going to spend as much on firearms as I have over the years, protecting them is worth the cost..The only problem with owning a bore scope is that it will bring out your anal qualities about barrel cleanliness...
 
My previous comment:Quote:I had that problem and thought my barrel was clean until I had it bore scoped and was informed that I had about eight inches of caked burned powder from the chamber forward....Took a lot of cleaning to get it out.

And another that just popped up by Acklyman:Quote:Being an old school benchrest shooter, I have been cleaning guns with good bronze bristle brushes for all my life. Ran into trouble some time back when a couple of custom guns got cleaned with patches only. Powder fouling caked up and got so hard it would not show black on patches, then the gun quit shooting...223 AI.

A couple of years ago, I worked up a home made electronic bore cleaning outfit for about $13.00,,,You might want to take a look at running something like that to cook out any baked on debris...It will insure that your barrel is clean and won't hurt the barrel...

http://www.predatormastersforums.com/forums/ubbthreads.php?ubb=showflat&Number=2615634
 
Originally Posted By: nr123 I can't get 60 rounds thru my Coopers without cleaning, more like 30. When shooting prairie dogs, my average is 25-30 rounds and need cleaning.

Can't get 60 rounds, without groups opening up to over 4 inches?????

That would be totally, utterly unacceptable to me for any rifle, but especially a p-dog rifle!

Cooper stuck you with some crap, right there. I'd bend their ear about it until they did something. At Cooper prices, you shouldn't have to put up with that kind of baloney.

- DAA
 
I would hope that my barrel has not fouled that bad at this point, but I do have some Wipe Out soaking in the bore right now. I will see how the patches look and go from there. I will take some fouler rounds with me when I make it back to the range. At least that way I may be able to narrow things down.
 
DAA, I learned from my fouled bbl while checking groups before a pd shoot. Shot some groups less than 1" at 300 yds. Shot at 200 yds, really opened up. They shooting at a target stapled to an IDPA target at 100 yds, didn't even hit paper. Copper fouling. After a good cleaning with WO, it was good to go.
If I was shooting at 4" prairie dogs, don't guess it would be a problem. But in my 12+ years of shooting them, never found any that big. Since I want to hit what I'm shooting at, guess I'll clean any time I get ready. I'm happy with my Coopers, and you can shoot what you want!
 
Guess so. I'd be very unhappy with Cooper for not doing anything about those barrels though, if it was me.

A decent .20 Prac barrel should easily go well over 100 rounds without getting even close to as bad as 4" groups. Honestly, it should go 200 rounds without groups falling apart like that. IF, if it has a "decent" barrel. Needing cleaned every 30 rounds for something with the capacity of the Practical, indicates a piece of crap barrel.

All my 20's have more capacity than that, the smallest being a couple .20 BR's, up to .20-250 and .20 Dasher. So they, in theory, should need more frequent cleaning than the Practical, burning much more powder and running much higher velocity. The BR's and Dasher are colony varmint rigs, so have had 100+ rounds through them without cleaning on a regular basis. One of the BR's has gone 200 rounds in a day, without cleaning, several times. All were still making consistent hits on p-dogs and 'chucks and were not difficult to clean afterward. Just some of my experience with .20's.

Your frequent cleaning required situation just doesn't have to be that way and for what Cooper charges you shouldn't have to live with it. I'd be pretty upset about it, if it was me. Just my opinion...

- DAA
 
Originally Posted By: TaterTotNot real sure what happened yesterday. I loaded up some 39 grain BlitzKings for my 20 Practical AR over IMR 8208. I shot the first round of charges at 25 grains and ended up with the following group:



I had subsequent charges loaded at 25.2, 25.4, and so on in .2 grain increments. The groups from the next three charges all looked more like a pattern of 00 buck shot. I'm talking 4" + sized groups.

My barrel is supposed to be an 11 twist, but I haven't checked it yet to verify that. I do have a load with 35 grain Bergers that shot really well, but I didn't have them with me at the time to see if they still grouped like they should. I might be able to shoot a quick group with them tomorrow.

I'm thinking maybe a scope issue, but if it's not the scope, is there something else on the rifle that I should look into? I did check the rings and scope mount while I was at the range. Everything was tight.

Any suggestions? Barrel nut torqued properly?
 
Barrel nut was torqued properly when it was installed. I wouldn't think that it could loosen up and back off without causing other issues. The gas tube goes through this particular barrel but, so I would expect some cycling issues if that was the case.
 
My 20 caliber AR's never did settle down with IMR 8208 especially with heavier bullets. Wound up using RL 10 & X-terminator & solved all problems. RL 10 & the 39's were very accurate.
Jim D
 
Finally got back to the range to check my rifle with a known good load. My 35 grain Berger loads shot like they did before: Pretty much 1/2"-3/4" groups.

So I shot a couple more groups with the 39 grain Sierras. Same problem..... Guess my rifle doesn't care for them, or at least not with the 8208 powder. I might try the 40 grain Vmaxes at some point, but for now I think I'll just stick with the 32's and 35's.
 
TT...Not sure what kind of "shooter" you are so from the group you posted, and not knowing what kind of scale those rounds are hitting on..or your rifle set up as to bench, rests, etc,,,it's hard to make any kind of evaluation...

When I'm building test loads, I use a Lead Sled, or other solid rest that is strapped to the bench, with the rifle strapped down as well...I build a series of test loads using .1gr powder charge weights with a minimum of five rounds each charge...

This removes as much of the 'human' element as possible since all I have to touch is the rifle and there is no adjustment as to shoulder pressure, cheek weld, etc and my good loads will produce groups in the .3s, or less...The scale on these targets is 1/2 inch..

These were shot without the use of the Lead Sled, just a front and rear bag

 
Turtle, that's some really nice groups. I've got a couple questions for you. What barrel & twist are you using? Do you prefer 748 or X-Terminator? Just built a new one with a 24" WOA 1-10 twist but haven't shot it yet. Tater, good luck with your venture. I feel sure you'll find a powder that will sling the 39's for you. I sure would try some RL10.
Jim D
 
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