Model 1 upper test fire question

[Autosear518]

New here and hope im not beating a dead horse with this question. I have an SSK Remington 700 bolt gun with an SSK suppressor. I bought a Model 1 300 whisper kit and built it into an AR about a week ago. The rounds I have for the 16 inch bolt gun work just fine. I am using subsonic 220 grain loads with H110 powder. I have yet to fire anything but subsonic through the bolt gun. I have been reading about throat dimensions and chamber differences with the Model 1 uppers. Obviously the quality of the Model 1 upper will not match that of the SSK bolt gun. So before I risk blowing myself up tomorrow I thought I would run some things past those with more experience in 300 AR platforms. The upper is stock just as it comes from Model 1. The rounds I have loaded so far are 150 grain Hornady soft point flat bases using 223 cases formed and trimmed to 1.352 with a variety of loads from 16.5 to 18 grains of H110. Due to chamber differences should I start with the light load of 16.5 grains of H110 and experiment with a shorter trim length? The reason for the trim length question is because i am using 223 cases and the chamber seems much tighter than the SSK bolt gun. I have chambered a fired case from the bolt gun into the AR and it felt pretty tight, but would still eject with minimal pull from the Chg handle. I only ask because of possible excessive chamber pressure from case length differences.

So with that said, i would like to know about experimentation with Model 1 uppers using 223 parent brass, various trim lengths and possible pressure problems. I also have AA#5, AA#7 and #9, Accurate 2015 but have had consistent luck with the H110 using JD jones load data. Thanks

[pug]

Don't try to use form fired cases in the AR until you get the feel for the gun. Some of the semi's will never work well with them. Full length size that same 1.352 case and it should drop and fall back out of the chamber with maybe only a little tap. The trim length should be fine but if the case is still tight in the chamber after full length sizing you may want to check it out more. After full length sizing and trimming seat a bullet in a dummy round and measure the loaded neck diameter. Most mil brass will run about .330 loaded and this should be fine. If you happen to have brass that measures .334 loaded your SSK rifle would shoot it but I would not shoot it in the AR (maybe an Oly but I would have to meaure the chamber first).

[Autosear518]

Thanks pug,
I was just using the fired case for comparison of an expanded case versus an unfired one. The cases I loaded all work through the action smoothly. Thanks for the input.

[Autosear518]

Range Report- The upper worked. The short trimmed cases would not always contact the exractor and the round had to be removed by tapping lightly with a cleaning rod. The subsonic rounds cycled (220 grain SMK with 8grains of H110). The transsonic rounds (150gr Hornady 17,18 grains H110) blew a lot of primers, probably 50%. The soft points deformed badly upon entering the chamber. The M80 bullets with the same load functioned fine but still blew primers. I will decrease loads and reply back. Please feel free to throw your $.02 in, any guidance would be appreciated.

[pug]

If you are blowing primers then the brass is probably a little sticky in the chamber due to the pressure. Back off and the cases will extract easier also. The trim length will not effect the location of the extractor groove as much as the head space. If the cases are going to deep then back off the die until the bolt won't close on a sized case and then turn the die down gradually until the shoulder is bumped back far enough the bolt will just lock. This will give perfect headspace for a bolt action but the AR bolt likes a little room to turn so turn the die down just a hair more. If you know all this just disregard .

[Autosear518]

Didn't know that, by back off i would assume you mean the powder charge. I just didn't want to go too low on the powder charge. I will drop it down to 16 grains and give that a try. Thanks for the info on the shoulder length.

[pug]

I looked up Hornady's 300 whisper load for their 150gr bullet and their max recommended charge of H110 is 16.2gr. Whether this is truly the max load for your gun you will have to decide.

[Autosear518]

Thanks, will try it tomorrow and give a report