220gr SMKs not stabilizing.

[MadDog]

Well, I tried some more loads. Some 220gr SMKs at around 1100 fps, Some 220gr round nose at about 1025, and some 240gr SMKs at around 1140 fps. None were stabilized at 100 yards. I did try some 190gr SMKs at around 1020fps that did stabilize and the accuracy was much better. I still don't know why the longer bullets will not stabilize out of my 1 in 8 twist barrel.

One issue that I noticed that may or may not be related. When I cleaned the upper the first time, I noticed a lot of small copper particles on the bolt and inside the carrier. This time when I cleaned it, there were no particles of copper but there is a considerable build up of copper on the bolt and inside the carrier. I will attach some pictures below. The barrel itself is cleaning up very easily with very little copper.

I have never seen that type of build up on my 223 uppers. Is this common with subsonic loads? I am shooting suppressed if that matters.

Any ideas?






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Looking for some advice- what would you do next?

I purchased a new 300 Whisper upper several months ago and just finally found time to start loading for it. After reading my manuals and posts here and on other sites, I decided on a couple of starting loads. My goal was to get 220 gr SMKs as fast as possible but still be subsonic. My barrel is 10" and has 1 in 8 twist.

I took the rifle out today and tried out several loads. None of them stabilized very well. I was pretty disapointed. I really thought that the 1 in 8 twist barrel would handle the 220gr SMKs without any problem. I will add a couple pictures of targets that include the load and speed of the rounds fired. As you can see the accuracy was pretty poor also. Since I am using a suppressor, I tried some of these at short range without the suppressor and they appeared stable at about 10 yards. Also I tried some at 100 yards without the suppressor and they were the same as the groups pictured.

Shouldn't they be stable at these speeds in a 1 in 8 twist? I could go a little faster but they were pretty close to being super sonic already.

Any suggestions besides trying different bullets?

Thanks,

Joe

[jjmcrowell]

You might try and make sure it's really a 1:8 barrel. Perhaps take a cleaning rod with a tight fitting patch, insert it and mark the position with a marker on the rod. Then slowly push it through the barrel, noting the distance till the muzzle and how many times it rotates. Just guessing, but if it's a 10" barrel and the chamber is 1.4" long it should have rifling a little over 8" long...this should give you 1 complete rotation of the cleaning rod. If you get less than one rotation, perhaps it's a 1:10 barrel.

I think a 1:8 should have no trouble with 220gr bullets.

[MadDog]

Originally Posted by jjmcrowell

You might try and make sure it's really a 1:8 barrel. Perhaps take a cleaning rod with a tight fitting patch, insert it and mark the position with a marker on the rod. Then slowly push it through the barrel, noting the distance till the muzzle and how many times it rotates. Just guessing, but if it's a 10" barrel and the chamber is 1.4" long it should have rifling a little over 8" long...this should give you 1 complete rotation of the cleaning rod. If you get less than one rotation, perhaps it's a 1:10 barrel.

I think a 1:8 should have no trouble with 220gr bullets.

Man, that is the first thing I did when I got home from the range. I thought the same thing- some one screwed up on the barrel. I did just what you described, twice. It is 1 in 8 for sure.

Any idea why it would not stabilize those bullets at those speeds?

Thanks,

Joe

[THE DOCTOR]

i do not know I have a 1/8 and i have no trouble stabilizing 240's so the 220 for you should be no big deal, but I am running a 16" barrel so that might make a difference too. You might try lapping the bore. I have heard good things about that.

[Pitt300]

Whose barrel is it?

[JFettig]

How does the muzzle look? If the crown is off it could be throwing the bullet off.

like pitt300 said, who made the barrel?

Jon