vaalpens said:
My question is. If it cycles the dummy rounds, there is no bullet setback, is there a minimum percentage of the bearing surface of the bullet that should be inside the case needed for bullet performance ... I would assume neck tension must have some impact on the bullet performance.
40S&W 180 gr TCFP or RNFP bullets have substantial bullet base that gets seated inside the case neck to provide better neck tension than 165/155 gr bullets, so even when using longer than SAAMI max length, I think consistent chamber pressures are being generated from sufficient enough neck tension as demonstrated by no bullet setback even after multiple chambering from the magazine (using harder 11-12 lead alloy for bullet core may be contributing to greater neck tension also).
Many match shooters switched from FMJ to JHP with the notion that shorter nose/hollow space in the bullet nose created longer bullet base for deeper seated bullet base (for more consistent initial chamber pressure build up) and longer bearing surface to engage the rifling for greater rotational stability and less wobble in flight.
Is this just theory or factual? The fact that many bullseye match shooters use JHP bullets over FMJ would support this notion.
When I saw that Missouri Bullet Company chose to go with "non-step" 9mm 115/124 gr RN to shorten the nose and increase the bullet base length, I smiled as Brad must have been thinking the same to increase the bullet base. Now, we see that Jake from Rocky Mountain Reloading did the same to the 45ACP 230 gr RN with shorter nose and longer bullet base ... smart thinking. If you are looking for accurate 230 gr RN bullet, you should definitely consider trying out RMR's 230 gr RN with longer bullet base.
As to 9mm, you'll see my struggle with longer OAL for less gas leakage vs more neck tension from shorter OAL in my 9mm load development and range test (maybe by next weekend as I haven't had a chance to take pictures of various targets from W231/HP-38, AutoComp and Titegroup). In my opinion, shorter 115 gr RN loaded to longer 1.160" may not produce enough neck tension to generate consistent enough chamber pressures unless you are using high enough powder charges. I think for this reason, many claim that 124 gr RN with longer bullet base are more accurate than 115 gr RN. Due to this, I usually load 115/124 gr RN to 1.135" unless I am using high enough powder charges.
Great shooting as always. I always wondered how you get these groupings since the it looks like a white blank target. What do you aim at at 25 yards? Do you aim at the previous bullet hole? You must have some great eyesight.
Well, I used to have better eye sight but in recent years, I had to resort to the aid of progressive lenses and slowly accepting the inevitable life's fate. For 10-15 yard testing, I do use the first hole as my reference mark. For 25 yard testing, I carry a bingo dauber in the range bag and place a dot where I want on the target (cheaper than round stickers and one dauber will last you a life-time). I try to focus on the front sight while using the dot as reference (recently, I find myself using bigger dots than before
) as POI will deviate from POA depending on the bullet weight/powder charge and I do not have adjustable sights on my Glocks as I prefer to keep them absolutely "bone stock" without even a trigger job so I can verify out-of-the box factory accuracy. As Walkalong and many others will admit, the shot groups in the pictures are the "best/smallest" of the shot groups shot. Some days I get tight shot group with the first 5 rounds but some other days, I need to shoot 6-7+ rounds to compensate for flyers (remember, I DO intentionally use mixed range brass). And yes, as range staff can verify, they are actual shot groups shot by me at specified distances.
It is for this reason why I am building a hard pistol rest like Ransom rest for retirement so I can test loads without being more frustrated by progression of life (I should just buy a Ransom rest but I like to tinker and need to justify the cost of Mig/Tig welders to my wife - and somehow I need to slip in a plasma cutter).