I will be curious as to the resolution of this. As the AI chamber is larger, firing a standard cartridge in an AI chamber should lessen the velocity of the bullet, as there is a greater volume for the same powder charge. I have never tested this, but the theory is consistent with PV=nRT. I don't know by how much the velocity will be reduced, AI cartridges tend to provide a couple of percentage more powder, but this is a low pressure cartridge.
Did you have tumbling issues before the AI conversion?
I would take your fireformed brass and load up some AI charges and see what happens. If the keyholing stops, then we have figured out, through trial and error, what the problem was. I can only remember keyholing issues when lead bullets stripped through the micro groove rifling, or in 308 Win, when the bullet was fired long range and tumbled on the way to the target because velocity was too low. Some bullet don't do well when transitioning through sonic speeds. Undersized bullets will tumble, so will bullets out of worn bores, I have seen both. Twenty five yards cannot be far enough to be having sonic transition problems, so something else is going wrong.
I am curious to know how reliably your action feeds those AI cases. I am a fan of cartridge taper, because they feed and extract well, AI cartridges are very straight, and if you have feeding problems, I would be interesting in knowing.
I do know, when testing my Marlin 30-30, that my rifle was very sensitive to velocity extremes. Loads which had wide velocity extremes shot poorly. Also, my rifle shot best when bullets went at factory velocities.
I conducted a number of tests trying to find the “best load” for my Marlin 336 carbine and at the end of it, I think I learned some things.
If you notice, my charges start with factory recommended loadings. I worked my way up and the velocities were low, very low. From what I have read, factory 170 grain ammunition should be between 2100 and 2200 fps. Maximum loads from the manuals gave me 1800, 1900 fps. I think this was because my chamber is huge, it may be as large as your AI chamber, so, maybe your results will be similar. After that I started at the top end of the manual and worked my way to three grains above the maximum loads, so note, my loads are over manual maximum. I never had any pressure issues. My cases were fired lubricated. This is a practice of mine as I have found that dry cases will take the load of the bolt disguising the signs of excessive pressure. I want sticky extraction when I reach maximum loads. Most of the time I used a coating of Johnson paste wax, for the 7 Feb data I coated every loaded cartridge with Kiwi Mink Oil shoe polish. This stuff provides almost effortless sizing, similar to Imperial Sizing Wax, so I was very sure that the full thrust of cartridge combustion would be applied to the bolt face. I never had any sticky extraction issues even though I was three grains above maximum with most powders. This trend was consistent with all the powders I used, so it is the gun, and I really don’t know why. I quit adding powder, either the case was full, such as with AA4350 or IMR 4064, or the groups got large and irregular, such as AA2520 and AA5744.
I noticed that the factory new cases all fell into my Wilson case gage to the proper depth. All new unfired rims were between “Go” and “No Go”. However, once fired cases are more than 0.02" “No Go”! If I had not lubricated the cases I am confident I would have experienced case head separations.
I also could not find the barrel throat. I loaded one case extra long, was able to insert it into the loading port, but found, I could not eject the round. Guess what, 2.550” is just at the maximum length that a loaded cartridge can have and still be ejected in this mechanism. It is all due to the ejector position in the receiver. The ejector locations limits the cartridge length; the ejector is forward of the rear opening of the port, an unfired cartridge has to tip out when the base hits the ejector. If the bullet is too far out it won’t clear the ejection port. I suppose it is possible to insert single shot rounds that are over 2.550”, but to remove them unfired from the rifle, you have to unscrew the lever screw, remove the lever and remove the bolt! This is, of course, impractical. It is my guess I was able to stuff in so much powder because my chamber is cut huge and the throat is a ridiculous distance ahead of the bullet. Given this volume to fill, what would be an excessive amount of powder in another rifle is just fine in this rifle.
As velocities changed so did the point of impact. A grain difference in charge would move the group as much as three inches. I would like to claim that there was a pattern to group size, but I could not figure one. I had some very excellent groups at 1800, 1900 loads with slow powders. Those same powders gave me blown groups at higher velocities. All groups were blown when the 170 bullet reached 2200 fps. As I scoped each shot I saw how the bullet moved up or down depending on chronograph velocity. This mechanism is extremely sensitive to changes in bullet velocities, the best powder, at the velocity I wanted, was N135. And I don’t think it is any coincidence that this powder gave the lowest extreme spreads in velocity.
The second best grouping was with IMR 4064, but only when velocities were close to 2100 fps. The extreme spreads were not as tight as N135.
Considering that a number of test combinations produced groups in the six inch group size, I was very happy to have a ten shot group that was 2.0” in diameter at 100 yards. The better groups were around 3.5” at 100 yards and were round.
I have a lot of 4350 powder and thought it would work in this cartridge and unfortunately, it did not . I could not get enough powder in the case to get meaningful velocities. I have no compunctions about heavily compressing 4350, but, unfortunately, I had issues with my bullet seater. The bullet seaters I used, RCBS and Redding, are tapered for spitzer bullets, not round nose bullets. Too much powder compression resulted in the round nose bullets being swaged into the bullet seater and I had to unscrew the bullet seater to pull the things out. If I had a 30 caliber compression die I might have been able to squeeze in another grain of powder to get meaningful velocities with 4350 and 2700, but a 30 caliber compression die I do not have.This powder might be worth experimenting in an AI chamber, but I would skip it and go straight to IMR 4064 and N135.
Code:
Marlin M336 microgroove barrel
150 gr Core-Lokt SP Remington Factory
29 Dec 2011 T = 56 °F
Ave Vel = 2255
Std Dev = 13
ES = 31
High = 2268
Low = 2237
N = 8
170 gr Hornady FBFP 30.5 grs AA2520 wtd lot 9595 W/W cases CCI200 OAL 2.545"
10 Jan 2014 T = 51 °F
Ave Vel = 1824
Std Dev = 67
ES = 160
High = 1933
Low = 1773
N = 5
170 gr Hornady FBFP 31.0 grs AA2520 wtd lot 9595 W/W cases CCI200 OAL 2.545"
10 Jan 2014 T = 51 °F
Ave Vel = 1852
Std Dev = 41
ES = 55
High = 1864
Low = 1809
N = 5
170 gr Hornady FBFP 31.5 grs AA2520 wtd lot 9595 W/W cases CCI200 OAL 2.545"
10 Jan 2014 T = 51 °F
Ave Vel = 1873
Std Dev = 40
ES = 68
High = 1883
Low = 1815
N = 5
170 gr Hornady FBFP 33.0 grs AA2520 wtd lot 9595 W/W cases CCI200 OAL 2.550"
14 Jan 2014 T = 50 °F
Ave Vel = 1986
Std Dev = 25
ES = 58
High = 2014
Low = 1956
N = 5
Last three shots good group
170 gr Hornady FBFP 34.0 grs AA2520 wtd lot 9595 W/W cases CCI200 OAL 2.550"
14 Jan 2014 T = 50 °F
Ave Vel = 2115
Std Dev = 35
ES = 87
High = 2143
Low = 2056
N = 5
2 ¼” group investigate further
170 gr Hornady FBFP 34.0 grs AA2520 wtd lot 9595 W/W cases CCI200 OAL 2.550"
7 Feb 2014 T = 40 °F
Ave Vel = 2117
Std Dev = 24
ES = 78
High = 2148
Low = 2070
N = 10
Group eight shots 3 3/8” X 1.5”
170 gr Hornady FBFP 35.0 grs AA2520 wtd lot 9595 W/W cases CCI200 OAL 2.550"
14 Jan 2014 T = 50 °F
Ave Vel = 2223
Std Dev = 24
ES = 53
High = 2250
Low = 2197
N = 5
poor group, easy extraction
170 gr Hornady FBFP 31.5 grs IMR4064 wtd lot 2449 W/W cases CCI200 OAL 2.545"
14 Jan 2014 T = 50 °F
Ave Vel = 1802
Std Dev = 12
ES = 24
High = 1812
Low = 1788
N = 3
poor group
170 gr Hornady FBFP 34.0 grs IMR4064 wtd lot 2449 W/W cases CCI200 OAL 2.550"
1 Feb 2014 T = 58 °F
Ave Vel = 2031
Std Dev = 20
ES = 50
High = 2064
Low = 2014
N = 5
170 gr Hornady FBFP 35.0 grs IMR4064 wtd lot 2449 W/W cases CCI200 OAL 2.550"
1 Feb 2014 T = 58 °F
Ave Vel = 2104
Std Dev = 30
ES = 68
High = 2122
Low = 2054
N = 5
group size 2.6 X 2.0"
170 gr Hornady FBFP 35.5 grs IMR4064 wtd lot 2449 W/W cases CCI200 OAL 2.550"
7 Feb 2014 T = 40 °F
Ave Vel = 2103
Std Dev = 20
ES = 64
High = 2128
Low = 2064
N = 10
group size 9 shots 3 ¼” X 1 7/8”
170 gr Hornady FBFP 36.0 grs IMR4064 wtd lot 2449 W/W cases CCI200 OAL 2.550"
7 Feb 2014 T = 40 °F
Ave Vel = 2135
Std Dev = 21
ES = 67
High = 2180
Low = 2113
N = 10
group size 2 3/8” X 2 ½”
170 gr Hornady FBFP 31.0 grs N135 wtd lot 901/98 W/W cases CCI200 OAL 2.550"
1 Feb 2014 T = 58 °F
Ave Vel = 1935
Std Dev = 17
ES = 45
High = 1953
Low = 1908
N = 5
group 1.5" X 1.2"
170 gr Hornady FBFP 32.0 grs N135 wtd lot 901/98 W/W cases CCI200 OAL 2.550"
1 Feb 2014 T = 58 °F
Ave Vel = 2029
Std Dev = 17
ES = 46
High = 2053
Low = 2007
N = 5
group 1.8" X 2.2"
170 gr Hornady FBFP 33.0 grs N135 wtd lot 901/98 W/W cases CCI200 OAL 2.550"
1 Feb 2014 T = 60 °F
Ave Vel = 2150
Std Dev = 61
ES = 42
High = 2146
Low = 2104
N = 5
group 2.3" X 1.0"
170 gr Hornady FBFP 33.0 grs N135 wtd lot 901/98 W/W cases CCI200 OAL 2.550"
7 Feb 2014 T = 41 °F
Ave Vel = 2081
Std Dev = 8
ES = 23
High = 2091
Low = 2068
N = 10
group 2 1/8” X 3.0”
170 gr Hornady FBFP 33.5 grs N135 wtd lot 901/98 W/W cases CCI200 OAL 2.550"
7 Feb 2014 T = 41 °F
Ave Vel = 2126
Std Dev = 9
ES = 31
High = 2136
Low = 2105
N = 10
2.0” best clustering
170 gr Hornady FBFP 23.5 grs AA5744 wtd lot $17.00 W/W cases CCI200 OAL 2.550"
1 Feb 2014 T = 60 °F
Ave Vel = 1910
Std Dev = 29
ES = 58
High = 1939
Low = 1881
N = 3
170 gr Hornady FBFP 24.5 grs AA5744 wtd lot $17.00 W/W cases CCI200 OAL 2.550"
1 Feb 2014 T = 60 °F
Ave Vel = 1978
Std Dev = 10
ES = 19
High = 1985
Low = 1966
N = 3
group 1 3/8" X 1.0"
170 gr Hornady FBFP 25.5 grs AA5744 wtd lot $17.00 W/W cases CCI200 OAL 2.550"
1 Feb 2014 T = 60 °F
Ave Vel = 2063
Std Dev = 17
ES = 33
High = 2083
Low = 2050
N = 3
170 gr Hornady FBFP 26.5 grs AA5744 wtd lot $17.00 W/W cases CCI200 OAL 2.550"
7 Feb 2014 T = 41 °F
Ave Vel = 2116
Std Dev = 28
ES = 75
High = 2153
Low = 2078
N = 10
Group 3 ¼” X 4 ½” blown irregular group
170 gr Hornady FBFP 33.5 grs AA4350 wtd lot 9-95 W/W cases CCI200 OAL 2.545"
10 Jan 2014 T = 52 °F
Ave Vel = 1710
Std Dev = 21
ES = 40
High = 1726
Low = 1686
N = 3
170 gr Hornady FBFP 34.5 grs AA4350 wtd lot 9-95, very compressed, W/W cases CCI200 OAL 2.545"
10 Jan 2014 T = 52 °F
Ave Vel = 1785
Std Dev = 26
ES = 47
High = 1815
Low = 1768
N = 3
170 gr Hornady FBFP 36.0 grs AA2700 wtd lot 18794 W/W cases CCI200 OAL 2.550"
1 Feb 2014 T = 60 °F
Ave Vel = 1979
Std Dev = 27
ES = 52
High = 2009
Low = 1957
N = 3
good five shot group two shots err1
170 gr Hornady FBFP 37.0 grs AA2700 wtd lot 18794 W/W cases CCI200 OAL 2.550"
1 Feb 2014 T = 60 °F
Ave Vel = 2059
Std Dev = 22
ES = 51
High = 2081
Low = 2030
N = 4
Five shot groups, one shot err1
170 gr Hornady FBFP 38.0 grs AA2700 wtd lot 18794 W/W cases CCI200 OAL 2.550"
1 Feb 2014 T = 60 °F
Ave Vel = 2102
Std Dev = 18
ES = 41
High = 2122
Low = 2081
N = 5
Best 100 yard targets: I recommend starting with these powders if you have them:
I was able to test my Marlin at CMP Talladega with my N135 load, and shot a 149.3 mm ten shot group at 200 yards with the best N135 powder. I expect that you should be able to find N135 powder in Germany, and I think this is a good powder to try in the 30-30 cartridge, even a 30-30 AI.
