Was able to get out this morning. Great shooting conditions, 45 degrees, slight (3-4 mph) north breeze, bright sunny day.
I have removed the forward recoil lug as discribed before and floated the entire barrel ahead of the rear barrel mounting screw. This test was to be a bit of a torture test from the beginning. Basically, I was going to heat the barrel up and keep on shooting for one simple reason, test my theory on why the double recoil lug was causing me problems, the barrel shank growing in length from heat expansion.
Set up at 1370 yards on a target rock that was just shy of 1 moa in size. I had not checked the rifle since fully disassembling the rifle to remove the forward recoil lug. First shot from a clean oily barrel was a dead center hit. Second shot landed 1 moa low. Shots 2 through 10 cut a single crater in the soft wet dirt. Obviously removing the forward lug solved the vertical stringing problem when the barrel heated up.
I then switched to the 250 gr Accubond test loads. They shot decently well at around 3/4 moa but not nearly as good as the 300 gr SMK at this range. Shot all 12 of those shots and then moved right to the 225 gr Accubond loads.
While the 250 gr load shot decently well, the 225 gr loaded to 3490 fps shot VERY poorly. 3-4 moa vertical variation and at least 2 moa horizontal. Very inconsistant. Even before I started shooting the 225 gr bullets the barrel was to hot to touch. By the time I was done with those test loads, I could smell the stock material as things got really hot.
I thought I may have toasted the throat so when I was done with the 225 gr loads, I took three more of my original 300 gr SMK loads and the Raptor dropped those three into the same crater as the first 9 shots. I was very happy to see that and very impressed. I have never shot a barrel until it was this hot, EVER. I am sure I wasted 500 rounds of barrel life in those 35 rounds down the barrel this morning but that was the test, a hot barrel torture test and with the 300 gr SMK it passed with flying colors.
So why did the 225 gr AB load shoot so poorly. I suspect that the Hybrid throat has eroded to the point that its simply not working with the relatively short baring surface 225 gr Accubond load. May also be an issue with the velocity they are being driven to but I suspect its the throat. I will clean the bore and get a good measurement on the origins of the rifling and I am sure that will tell me exactly what I am suspecting.
This barrel has around 400 rounds down the barrel and many of those were out of a warm or hot barrel trying to get a solid preformance record as the barrel heated up so while the actual round count is only 400 rounds, the wear to the bore is likely more like you would see on a 1000 round count barrel.
Again, if the hybrid throat is eroded enough, the slightly undersized AB bullets will have a serious issue with this throat so that may come into play when dealing with customers that want to use this bullet. My conventional throat may be a much better choice for this bullet. The ABs generally measure in at a full 0.001" smaller in diameter then a conventional cup jacketed bullet such as the SMK. Plus, because of their solid base design, they will not bump up under pressure like the SMK would to seal the bore and grip whats left of the eroded lands.
I was very happy to see the performance of the 300 gr SMK from an excessively HOT barrel. There was really no change in POI or accuracy from a cold barrel to a bedding burning barrel temps.
The barrel was so hot that the rear barrel mounting bolt was hot to the touch on the bottom of the stock!!!! And it remained warm to the touch even after I got home from the shooting session nearly 30 minutes later. Again, this was an extreme test for a barrel and about the best way to destroy any barrel but in some cases, it just has to be done to learn about a rifles performance, its limits and behavior throught the barrel temp range.
New barrels are on the way for more testing so I am not overly concerned. I will also be testing the muzzle velocity of the 300 gr SMK again just to recheck it. Originally it clocked an average 2980 fps. I suspect it will be a bit off this because of throat erosion.
When I get the results from checking the throat I will let you know. For the time being however, I am 100% convinced that I have solved the problems created by the double recoil lug design. I may test a barrel totally free floated from the recoil lug forward with no barrel mounting screws at all just to see if it will make any difference but I suspect I will have to shoot out to a mile with each system to be able to tell any difference if there is any as the Raptor today put 12 rounds into a crater that measured 3/4 moa in size outside to outside measured off my NF NP-R1 reticle 5.5-22x 50mm set on 22x. I will not say that the group was smaller then 3/4 moa but thats the size that the resulting crater was so the group size was smaller then that........ Very happy with those results.
As far as using the AB bullets, I believe in my conventional throated rifles they will work just fine but you may loose 75 fps from the Hybrid throat design but you will likely be able to use them the entire life of the barrel so you would see around 3325 fps with the 250gr and 3425 fps with the 225 gr AB. I still believe they would be more impressive on lighter game at ranges under 1000 yards and will test them in my Raptor Stalker when its up and running hopefully her soon. I think I have just been to hard on this barrel for the Accubonds with the Hybrid throat.
More to come.
