User Panel
User Panel
User Panel
UT, USA
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Posted: 6/13/2024 10:13:08 PM EDT
A friend of mine was asking me a question about cold bore accuracy on his AR-10.
He explained that consistently his first two rounds are low right or right depending on the temperature. He explained that with his rifle the hotter it got the more consistent it grouped. He asked me what my thoughts are but I am by no means an expert. Maybe you guys can give me some ideas to throw his way or maybe this is normal. He is a SWAT sniper but up until recently only shot a bolt gun for precision. Below is the rifle in question. Aero M5E1 308. 18" barrel suppressed. 1:10 twist. Bullet: federal 168 gold medal match. 2555 FPS at the muzzle. |
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Posted: 6/13/2024 10:46:03 PM EDT
[Last Edit: AeroE]
[#1]
Normal for a cold bore, clean bore to print out of a warm barrel group.
As a pro, he has to know this, it's not an option. He also needs to decide whether he will zero and shoot cold bore, clean bore shots, or cold bore, fouled bore shots. |
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Posted: 6/14/2024 12:39:02 AM EDT
[#2]
What AeroE said plus bolt guns act the same; maybe even more so since they are inherently more accurate (i.e. the differences in the shots will be more readily apparent).
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USA
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Posted: 6/14/2024 12:53:37 AM EDT
[#3]
In my experience this is normal for CHF and button rifled barrels. They retain internal stresses from the manufacturing process. As a result they change shape (beyond normal thermal expansion) when going from cold to hot.
Single-point cut rifled barrels can avoid this altogether because the blank is normalized to relieve stresses before the rifling is cut, and cutting doesn’t introduce stress like hammer forging or swaging a button does. Also, Criterion barrels do well. They are button rifled, but normalized afterwards to relieve internal stresses introduced by the rifling process. I have 2 cut rifled barrels and a Criterion barrel, and they have no shift in POI from cold to hot, but all my other barrels do to some extent. |
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Posted: 6/16/2024 5:23:51 PM EDT
[#4]
I’m just an armchair shooter but a gun that tightens up as it warms up suggests tolerances are a little loose. Having a round or two print slightly different ccb vs fouled bore is not uncommon. In my limited experience with high quality barrels ccb vs fouled doesn’t make much different. My GA Precision bolt gun and my custom Bartlien barreled 6Arc AR shoot the ccb rounds right with the fouled rounds.
It comes down to knowing your equipment and what you can reliably document and repeat on target. If the ccb is consistently printing in same place then it no problem to have that shift if you remember to apply it. |
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Posted: 6/17/2024 10:01:25 PM EDT
[#5]
Quote HistoryOriginally Posted By MemeWarfare: In my experience this is normal for CHF and button rifled barrels. They retain internal stresses from the manufacturing process. As a result they change shape (beyond normal thermal expansion) when going from cold to hot. Single-point cut rifled barrels can avoid this altogether because the blank is normalized to relieve stresses before the rifling is cut, and cutting doesn’t introduce stress like hammer forging or swaging a button does. Also, Criterion barrels do well. They are button rifled, but normalized afterwards to relieve internal stresses introduced by the rifling process. I have 2 cut rifled barrels and a Criterion barrel, and they have no shift in POI from cold to hot, but all my other barrels do to some extent. My 20” Bartlein shoots my zero/reference 77 TMK load to the exact same POI when clean and cold as when it’s hot and dirty. I love that barrel. |
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Posted: 7/14/2024 10:22:54 AM EDT
[Last Edit: ScoutH57]
[#6]
He needs to research what a cold bore group is. That’s LE sniper 101.
He probably just got lucky with his bolt gun, it’s absolutely possibly to have POI on cold vs Warm note be the same with some systems but it’s the exception not the rule in my experience. @Bentley66 IM me if you want me to nerd out fully. ETA didn’t realize how old this post was 
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Posted: 7/15/2024 10:21:00 PM EDT
[#7]
Quote HistoryOriginally Posted By ZA206: My 20” Bartlein shoots my zero/reference 77 TMK load to the exact same POI when clean and cold as when it’s hot and dirty. I love that barrel. Quote HistoryOriginally Posted By ZA206: Originally Posted By MemeWarfare: In my experience this is normal for CHF and button rifled barrels. They retain internal stresses from the manufacturing process. As a result they change shape (beyond normal thermal expansion) when going from cold to hot. Single-point cut rifled barrels can avoid this altogether because the blank is normalized to relieve stresses before the rifling is cut, and cutting doesn’t introduce stress like hammer forging or swaging a button does. Also, Criterion barrels do well. They are button rifled, but normalized afterwards to relieve internal stresses introduced by the rifling process. I have 2 cut rifled barrels and a Criterion barrel, and they have no shift in POI from cold to hot, but all my other barrels do to some extent. My 20” Bartlein shoots my zero/reference 77 TMK load to the exact same POI when clean and cold as when it’s hot and dirty. I love that barrel. This is my experience as well with my 18in Bartlein |
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Posted: 7/20/2024 10:39:45 AM EDT
[#8]
Quote HistoryOriginally Posted By AeroE: Normal for a cold bore, clean bore to print out of a warm barrel group. As a pro, he has to know this, it's not an option. He also needs to decide whether he will zero and shoot cold bore, clean bore shots, or cold bore, fouled bore shots. <This Changing bullet brands and even powders will take several rounds for a barrel to settle in, even if already dirty. The different jacket material and powder chemistry will have an effect on groups size and location. Cold bore zeroes are rarely the same as shots fired through a rifle that has rounds fired down the tube, unless you fire two or three fouling shots after cleaning the rifle. Many people have recorded as much as 100 fps higher velocity from a clean cold bore compared with the following rounds fired. Every serious competitor or military/police sniper keeps a DOPE card (Data On Previous Engagements) so they have a working history of their rifle's actual performance on target. It's the shooter's responsibility to know how his rifle/ammo combination behaves and to adjust his hold or scope settings to offset the known zero changes. |
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Posted: 7/28/2024 8:55:37 AM EDT
[#9]
Quote HistoryOriginally Posted By borderpatrol: <This Changing bullet brands and even powders will take several rounds for a barrel to settle in, even if already dirty. The different jacket material and powder chemistry will have an effect on groups size and location. Cold bore zeroes are rarely the same as shots fired through a rifle that has rounds fired down the tube, unless you fire two or three fouling shots after cleaning the rifle. Many people have recorded as much as 100 fps higher velocity from a clean cold bore compared with the following rounds fired. Every serious competitor or military/police sniper keeps a DOPE card (Data On Previous Engagements) so they have a working history of their rifle's actual performance on target. It's the shooter's responsibility to know how his rifle/ammo combination behaves and to adjust his hold or scope settings to offset the known zero changes. A lot of truth in this post. I have seen enough examples of shooting one OEM factory load after another, and watched groups shrink as the rounds season in the bore. Can I tell you specifics.. No, but it has happened enough to consider it reality. FWIW... CMP had a list of what powders not to use after another and vice versa... just from seat of the pants results. ( Before all the modern tech ) As an example... Powder Compatibilities Short Range Long Range OK? 2015 H4350 No 4895 N540 Yes AA2520 N540 No AA2520 N135 No IMR4895 Re15 Yes IMR4895 Varget No IMR4895 IMR4064 Yes IMR4895 H4350 Yes IMR4895 N540 Yes H4895 Re15 Yes N135 N540 OK, No N135 N140 Yes N135 N150 Yes N140 N540 No N140 H4350 No N140 Varget No N540 N550 Yes N540 IMR4895 No Re15 N540 Yes, No Re15 N550 Yes Re15 N140 No Re15 Varget No TAC N135 Yes TAC N140 Yes TAC Re15 Yes TAC IMR4064 Yes TAC Varget No Varget N540 No, Sighters low, rest OK. Varget H4350 Yes Varget N140 Yes Varget IMR4064 Yes WC844 Varget No WC844 Re15 No WW748 Re15 No IMR4064 N150 Yes |
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