Okanogan
Well-Known Member
There has been a considerable amount of discussion recently since the PRB series about throat erosion and jump. I've been working up load for a new GAP 6.5 SAUM and for the most part enjoying the journey trying out some of the PRB ideas. I have had mixed success with groups ranging from 0.3 MOA to 0.5 MOA for what I considered the "good" loads. (and of course I have had much less successful loads along the way). I have about 225 rounds through the new barrel and so consider it more or less broken in.
Before I fired any rounds through the new rifle, I stripped the bolt and used the Wheeler method to set up reference cartridges for bullets that I was interested in testing out with the new rifle. Today I stripped the bolt again and repeated the exercise of determining distance to the lands for several bullets. Here are my results:
156 gr Berger EH initial COAL 2.861 to lands/ current COAL 2.929 to lands
140 gr Berger EH initial COAL 2.956 to lands/ current COAL 2.958 to lands
147 Hornady ELDM COAL 2.774 to lands / current COAL 2.801 to lands
I know a lot of folks think COAL sucks vs measuring to the ogive, but these are the same bullets in the same original reference cartridges. My initial thought was I must have really screwed up the Wheeler test for the 156 EH but I will say in my opinion there is no way you could screw it up by more than 0.060 and not notice, that and 156 EH are the best shooting bullets in the new rifle.
My current hypothesis is I think some bullet shapes are more inherently susceptible to changes in throat erosion in terms of bullet jump than others because of their geometry. (i.e. a really tapered bullet may be more affected than a less tapered bullet) I would have considered both the Berger bullets above to be pretty tapered so this theory might be worthless as the change in COAL are really different. I know it is possible that I blew the COAL for the reference round on the 156 EH but that still wouldn't really seem to explain the relatively small change for the 140 Berger EH vs the ELDM which is not nearly as tapered as the Bergers.
The PRB articles on bullet jump and throat erosion were pretty interesting to me because I really had never consider throat erosion very much in my reloading practices. I'm sure some bullets are more forgiving than others on jump, but I wonder if some bullets are inherently more tolerant/ susceptible to throat erosion than others. I've seen some pretty insightful comments recently from Alex Wheeler, et al. I'm interested in feedback on the above information and what it might all mean in the context of the PRB articles.
Before I fired any rounds through the new rifle, I stripped the bolt and used the Wheeler method to set up reference cartridges for bullets that I was interested in testing out with the new rifle. Today I stripped the bolt again and repeated the exercise of determining distance to the lands for several bullets. Here are my results:
156 gr Berger EH initial COAL 2.861 to lands/ current COAL 2.929 to lands
140 gr Berger EH initial COAL 2.956 to lands/ current COAL 2.958 to lands
147 Hornady ELDM COAL 2.774 to lands / current COAL 2.801 to lands
I know a lot of folks think COAL sucks vs measuring to the ogive, but these are the same bullets in the same original reference cartridges. My initial thought was I must have really screwed up the Wheeler test for the 156 EH but I will say in my opinion there is no way you could screw it up by more than 0.060 and not notice, that and 156 EH are the best shooting bullets in the new rifle.
My current hypothesis is I think some bullet shapes are more inherently susceptible to changes in throat erosion in terms of bullet jump than others because of their geometry. (i.e. a really tapered bullet may be more affected than a less tapered bullet) I would have considered both the Berger bullets above to be pretty tapered so this theory might be worthless as the change in COAL are really different. I know it is possible that I blew the COAL for the reference round on the 156 EH but that still wouldn't really seem to explain the relatively small change for the 140 Berger EH vs the ELDM which is not nearly as tapered as the Bergers.
The PRB articles on bullet jump and throat erosion were pretty interesting to me because I really had never consider throat erosion very much in my reloading practices. I'm sure some bullets are more forgiving than others on jump, but I wonder if some bullets are inherently more tolerant/ susceptible to throat erosion than others. I've seen some pretty insightful comments recently from Alex Wheeler, et al. I'm interested in feedback on the above information and what it might all mean in the context of the PRB articles.
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