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rsterne
There has been enough experimenting in recent months that a clear path is forming regarding what diameter cast bullets (including BBTs) or swaged slugs to use if your airgun barrel is choked at the muzzle because it was intended for diabolo (waisted) pellets…. You cannot measure the groove diameter at the chamber and use that, and be guaranteed of good accuracy…. The key seems to be to measure the groove diameter at the muzzle, where a choked barrel is the smallest diameter, and size to the groove diameter at that point…. You may still need to play around with slight changes, up to a thou either side of that, for best accuracy in your barrel with any given bullet…. but that is certainly the place to start….
If your barrel is not choked (ie the same diameter breech to muzzle), then start with the groove diameter, and experiment from there…. MOST shooters seem to be finding the best accuracy when bullets are sized slightly under that diameter (typically 0.0005-0.001″)…. This is in contrast to what is typical in the PB world, where sizing bullet just over the groove diameter is common….
Bob
rsterne-
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rogerhaun
One way is a series of gauge pins, they come in 0.001″ increments…. find the largest one that slides into the muzzle without resistance…. Don’t force in a larger one, you could damage the rifling…. The problem is, that will give you the land diameter, not the groove diameter, which is what you really want…. I have had some success with pushing an oversize lead bullet into the muzzle (leaving some protruding), pulling it back out, and measuring the OD with a micrometer…. I do 2 or 3 to make sure I get the same reading each time….
The most common way is to push a pellet through the bore all the way from the breech with a cleaning rod, catching it as it exits the muzzle…. This mimics what happens on firing, but in a very gentle fashion…. If the OD of the head and skirt measure the same, then that is the measurement you use for the groove diameter…. If the head measures smaller (and doesn’t have any marks on it between the rifling lands), then you have to use the diameter of the skirt…. If you have a soft lead bullet or cylinder you can use that, but if it is too big, it will be too hard to push through the bore, and you could even jam it in….
Bob
Ok Bob I was able to push a NSA slug through my LW barrel I knew it would be some what tighter than a pellet because of more contact surface and it was but when I got to the choke it was extremely tight! I got it through and was surprised at the result. The slug was .250 after it came out it measured .2485 so I assume I should use a .249 push through air gun die I would think you would not want the bullet smaller than the choke? I will be using the Lee single stage press (md90045) I assume this press should work. I am not sure just what I need from NOE. I know I need a air gun push through sizing die, air gun push rod in 25cal but I am a little confused on the push through size die body (PTSD01). Do you order just the one that is needed or is it a kit for $39.95?? This is all new to me but looking forward to getting started. Please review what I need to order to get started and it me know if it is correct. I do appreciate any help
You will want the
PTDS01PTSD01 die body set (does all calibers with appropriate bushings)…. and I would get both a 0.249″ (B249AG) and 0.250″ (B250AG) bushing…. and a .25 cal airgun pushrod (25PRAG)…. That should work with your Lee press…. The nice thing is that all you need in future for other calibers is the appropriate body bushings….Bob
Thanks again for all the help Bob. I was sure it was a typo, just had to make sure. I have one more question for you then I will leave you alone for a while but if I do not ask question I can not learn. Do I need to lube the slugs before I size them? What should I lube with? Sorry that is two questions. I will get this all ordered and size the slugs and test and let everyone know how it went on this forum and GTA. It may be a while before I will know how they shoot because I am in Indiana and the weather sucks here right now!! Thanks again for all the help.
I have never lubed my bullets, but some guys do…. I use a wax lube (in trace amounts) that I brush through the sizing die, it just eases the passage of the bullet…. I believe it is RCBS or Hornady case wax?…. After sizing about 20 bullets you can feel the resistance increase and I run the brush through the die again…. It’s like lubing a case neck for sizing….
Bob
Got all the equipment that I needed to size the NSA slugs. Everything went well it was a little strange that there is always a few left in the push through tube guide. I sized the 34.7 and the 39gr. slugs to .2487 using the 249 sizer they tend to size just a little under size I think I read that somewhere no big deal. now for the groups I was only able to test the 34.7 slugs. I tested both the sized and unsized slugs filled to the same pressure with each test. The sized slugs shot 3/8 inch smaller vs the slugs that were not sized. The test was done a 50 yards the sized slugs shot right at 1/2 inch. I am sure I can get better tighter groups If I do my job. I will take it out to 100 yards in the spring. Now I have a question for you Mr Bob should I play around with the velocity. I shot some over the chony and I am in the mid 900s. I was thinking about lowering the velocity? Also I may size down one more time. What are your thoughts? I feel that I will be able to achieve 1 inch groups at 100 yards. Please give me your thoughts on this . Thanks again
You can experiment with the velocity…. but if you get an improvement in group size that may have nothing to do with the velocity per se…. but rather a change in the barrel harmonics…. or rather how that affects the group size because the bullet is arriving at the muzzle at a different time during the barrels vibration cycle…. Only by using a harmonic barrel tuner and adjusting it for the smallest group with every velocity change…. and then comparing THOSE groups…. could you state it was the velocity that made the difference….
Bob
rogerhaun
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