Best method to use to see if a rifle barrel is shot out?

[MarkCO]

Just FYI, that happened to a lot of people, a few much worse.

[kurtm]

How strange, a barrel that groups well cold and then scatters when hot....I've never heard of such a thing.

[GetAwayDriva]

I'm certainly not qualified to post here, but thought I would share my experience. My rifle would group just fine at 100 yds. 1 Moa or less. But I was struggling with 300 yds and out. I just figured I was a sucky rifle shooter. But I put it on paper at 300 yards off a good rest just to see what it was doing and the groups were huge. Like 6-10". I was still pretty sure it was just operator error since I am not a very good rifle shooter but I decided I wanted a longer barrel (had a 16" on it) so I ordered a JP barrel. When we pulled off the old barrel, it was quite apparent it was not operator malfunction. There was absolutely no throat left in the barrel!

[openclassterror]

I have seen the cold= good hot= bad phenomenon fairly often when shooting bullets with a marginal twist. The big fad a decade ago or so in benchrest was to use the absolute slowest twist that would stabilize your bullet weight. Cutting it close enough that changing from a flat-base to a longer boat-tail in the SAME weight would keyhole. The theory espoused was that spinning any faster than necessary was bad juju. This thought has fallen by the wayside as real life didn't support the theory. What WAS learned was that seemingly minor changes (like 50fps velocity change) might be enough to de-stabilize said projectile. I had a barrel on my PPC at one time that would group outstanding at 300 yards on a cool fall morning, but produced shotgun patterns on the target on a 95 degree summer day with the same bullets.

In respect to ARs, I have had more than one 1-8 twist barrel that shot good cold groups with 75-77gr bullets but poor hot groups. Both grouped much more consistently hot/cold with 69s. 1-7s seem less sensitive with 77s in general.

As I stated on another thread a while back, it is more important to me to have a barrel/ bullet combination that shoots a maximum of 2MOA clean or dirty, hot or cold, than one that shoots 1/2 MOA cold and clean but scatters or moves POI when hot. Some match directors that like to torture cold-bore shooters deliberately place the long range engagements at the end of the rifle section so the gun is good and hot when it is time to stretch out.

[kurtm]

Well that must be it Tom! Both Chris's rifle and mine were J.P. CTR-02 with 1X8 twist barrels shooting 55 grain bullets. I must need a lot more twist for those 55 grain Sierra ballistic tips, what twist would you recommend for such a bullet? Should I go to a 1X7? Maybe a custom twist for such an odd ball bullet?

[openclassterror]

I was simply stating a set of circumstances under which such a phenomenon occurred that I was a personal witness to. At this year's Ironman match, I watched as a friend's BHW barrel went from sub-MOA a few days prior to full keyholes with every bullet weight from 55 to 77. Less than 10k rounds through it. No visible damage to the crown, minimal throat erosion (for 10k). Did exactly the same when we returned, regardless of what receiver we used, gas block, no gas block, free float fore end, NO fore end. To this day we still don't know why it went to hell, no logical explanation. I was only stating a case in which the circumstances led to a discovery of cause. Lots of internet experts (here and elsewhere) that can diagnose gun ailments over the web. I ain't one. Your sarcasm was amusing, though

[kurtm]

I guess that is the point. As you state, you have seen barrels that group well cold and then don't group well hot. Now this is EXACTLY what I have been trying to say. The O.P. was advised that the best way to determine if a barrel is shot out is to see how it groups cold. My contention was if it scatters ( note, not just opens up) when hot....it is shot.......out that is. EVEN IF it groups well cold. As you point out lots of experts were telling him all sorts of stuff, and some were telling him all sorts of stuff was wrong with his rifle. I still contend that a hot group is much more telling than a cold one, and you yourself eventually mentioned you had seen this phenomenon.

[Tom Freeman]

After 12K I would assume it is gone.

Lets go to the range and get it warm (like at a match) and then shoot some groups at 300/400 and 600 and see how it does.

I will bring my borescope so we can also take a look inside.