Put together a 308 puma rifle with a 30" bbl to shoot hv cast/traditional lubed/pc'd bullets. One of the things I was interested in the pc coating and if it "seasons" the bbl. And what that seasoning/coating of the bbl does for accuracy, poa, etc. This is only the 3rd outing with the new bbl on the rifle. The 1st outing was only testing the function and checking the setting the head space to make sure the brass's shoulder/neck area wasn't being overworked. The 2nd outing was to start to form a baseline for feedback such as bullet stability, dispersion, get an idea of velocity/pressure for loads,etc. Was surprising to get a 2" 10-shot group with 2650+fps pc'd bullets.
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Finely got time to get back out and do a little more testing. This time I brought a bore scope and took some pictures. Started with a clean bbl and did a 10-shot group with rl19 to season the bbl (left). I left off at 37gr of h335/lee 160tl bullet on the last outing and wanted to test a 38gr load and a 39gr load. The 38gr load looked good, (center) and did a 2" 2718fps 10-shot group. The 39gr load opened up to 2 1/2" doing 2786fps 10-shot group.
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At this point I could care less about groups, these initial outing are giving me excellent feedback. I need to bed another 1" of bbl. Change the scope rings over to high rise from the mediums, I put the mediums on because I was using the rifle to shoot prone. And lastly, change the rear bag. Doing this will tighten the groups up to show changes in the bbl from coating build-up.
I started the session off with a clean bbl. This bbl has never seen a jacketed bullet, only cast pc'd/lubed bullets and al gc's. It has never seen a metal brush either, only nylon brushes. A picture of the bbl's throat. The bbl shined the entire 30" length
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This bbl is extremely smooth. When I had it out for it's 2nd outing/range session I shot traditional lubed bullets to season the clean bbl. It took 14 shots to get a star pattern on the muzzle of the 30" bbl. Side note: As you can see in the picture, I bedded the bbl high. That allows the bbl to cool quicker and be less affected by forearm pressure (sling). The trade-off is less bbl support, hence the need to bed another inch of bbl. 2nd side note: Need to start using a real rear bag instead of a block of wood and a royal crown bag.
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After shooting 30 rounds of some pretty hot/hv pc'd bullets I took pictures of the bbl. The throat was spotless. I started to see black streaks at around 6"'s back from the throat.
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At the 15" mark/middle of the bbl.
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At the muzzle end of the bbl.
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It took 1 wet patch and 1 dry patch of bore tech to bring the bbl back to spotless.
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I need to get the rifle dialed in so I can test to see how the different affects I do to the bullets impact the target (group & poa). Things like testing a .308/.309/.310 bullet come to mind. I'm shooting .311 bullets right now. Perhaps a 2nd coat of pc? Don't know & actually at this point I'm really leaning towards seasoning the bbl with an even coat the entire length of the bbl and seeing what happens. I've done 500+ round tests with pc'd bullets in pistols and they held the same accuracy thru the whole range session. But those were only 25,000psi/1100+fps loads. These rifle loads are in the 36,000psi range & running 2600fps+.
Anyway, saw there was some talk about black streaks/build-up in rifle bbl's when shooting hv/high pressure loads with pc'd bullets. Figured I take a bore scope to the range and have a look between 10-shot groups and post some pics. Unfortunately I need to get the rifle dialed in to get rid of the horizontal strings to be able to tell if there's any subtle differences in the bbl as it gets seasoned/coated.
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Originally Posted by oteroman
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