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Posted: 5/27/2008 7:33:48 PM EDT
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Here is the Scenario. S&W MP15T Cold weapon: first shot 2 inches right of center vertical dead on, Warm Weapon: 1 10 rnd mag shot....wait 15 min. Same as above. Hot Weapon: just the time to change mags....All shots dead on. This is with a variety of hand loads and factory. Clamped into a bench rest. Same results hand held with sandbags. I have 2 of these...only one exhibits the problem. I would have went to the industry forums but it would appear that there is no S&W forum. Any help would be appreciated. Tiger |
First of all, use the same ammo for all tests. Then you can rule out that being the problem. And like the person above stated, what range was this at? |
I might buy that except it was WAY too consistent. And the second rifle NEVER exhibited this behavior to any degree....in the tests with the second rifle clamped in, with my best performing hand loads it was a dime to nickle sized group. As was the first rifle test EXCEPT for that first shot 2 inches to the right but only when there was cool down time. I am thinking it has to be something heat related but just not sure what.... |
| That is the classic symptom of a barrel blank that was straightened somewhere during it's manufacture. As soon as the barrel gets heat in it it reverts to the prestraightenend POI. Many barrels exhibit this. Premium barrels that have never been straightenend and advertised as such should shoot to the same POI hot or cold. You just need to keep a mental not as to where the cold shot goes and zero for the warm. |
This was my first thought too. So we tried various methods including but not limited to bolt release first feed, full mag with bolt at battery and pulling the charging handle back, Hand feeding each shot....all with the same results give or take an 1/8th to a quarter of an inch at 200 yds. |
Interesting, I really had no idea they would "straighten" a blank, I guess I assumed they would toss it if it wasn't spec. |
If you ever see them do it in person you'll kringe. There's a video somewhere on the net of FN straightening their barrels for the M16A4. |
I work for a company who heat treats a lot of steel including a few rifle barrles, and I can assure you it has nothing to do with being "in spec". When steel it heat treated, it warps. It has to be straightened back out. |
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It’s the cold barrel shot and to a sniper that’s the one shot one kill. As the barrel warms, it changes slightly so the follow up shots hit a different area on the target but consistently. There can also be a difference with a hand chambered round to one auto loaded from the mag. Shot one round wait 3-5min shoot again, repeat and record the results. Always remember to keep things consistent when zeroing. Same ammo and same rest. |
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I'm not a real AR expert (most of my experiance is with bolt guns and single shots) but what you described is a textbook case of cold barrel vs warm barrel. Your case is also a little excessive. You can try the barrel fully free floated to see if that changes anything for better or worse. If it improves great! If it stays the same or gets worse, your only recourse is to replace the barrel with another one or a higher quality one. The issue is stress in the metal itself. It can be stress releived but that runs the chance of warping the barrel and would be expensive. ML Gray |
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