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NEW 7 SHERMAN SHORT TACTICAL (SST)
- Thread starter elkaholic
- Start date
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SteelBanger
Well-Known Member
Soon! My smith forgot to send my trigger back with my barreled action so I've been waiting since 12/9 for that to be shipped back ... UPS just delivered it this morning though so hopefully I can get out and shoot some initial loads within the next week or so. We have about 1/4" of ice and a few inches of snow on top of it right now so not great shooting conditions unfortunately.
SteelBanger
Well-Known Member
Got it all put together today! It's going to be around 20° in the morning but I'm hoping to get out and put some rounds down the pipe.
I have 200 cases to fireform so I won't get to max velocities anytime soon but excited to finally squeeze the trigger ... been about 13 months since I started buying parts.
elkaholic
Well-Known Member
Lookin good!
archangel485
Well-Known Member
@SteelBanger, I'm a little ways behind you but I do have my barrel torqued on my rifle and all of my ammo components. The only thing I'm currently waiting for is Forster to send my die back to me, I should hear from them today or tomorrow on what they found. I was getting a lot of runout, like 10 thousandths, so I stopped sizing brass. They are going to hone it out which by itself should reduce runout, but they're also going to check it with a couple pieces of un-sized brass I sent them to make sure the expander ball is in the right place etc. My brass is the not needing fireformed version so I should be able to get straight to doing ladders I believe, correct me if I'm wrong @elkaholic. I actually looked up this thread today so I could get some starting load data so thank you and Rich both for the info. I will be shooting 180 hybrids powered by RL26 and BR2 primers. I imagine I will get my die back and hopefully have time to develop and shoot some ladders in the next month. My goal is by end of Feb to have a load fully developed and get a couple hundred rounds loaded up to start practicing/collecting drop data.
archangel485
Well-Known Member
Well I still haven't heard from Forster and have gotten no response to the two emails I've sent. I will call them if I don't hear soon. Regardless, I had about 15 pieces of brass I had sized prior to realizing how awful the runout was, so I was able to get my barrel break in complete. I have a ladder test loaded up and plan to run through that in the next week or two as well. @SteelBanger, how is your shooting going?
SteelBanger
Well-Known Member
I had initially mistakenly sized my first 50 pieces of brass too far which gave me too much headspace (different thread on the FB page for that), When I last went to shoot I thought I had pushed the bullets out far enough to hit the lands and prevent the case from moving forward with the firing pin but apparently I was still a little short and still got light primer strikes. I've pulled the bullets out to where I'm 99.9% positive they're sitting on the lands but I haven't had the chance to get back out again to fire them. Luckily I took one of my AR's out on that last range trip so I was still able to get some shooting in, but I was super disappointed to not set off any of these 7SST rounds. Hopefully this weekend!
archangel485
Well-Known Member
@SteelBanger based on your post I believe I may need some education. How would either over sizing the brass, or seating the bullets too deep allow the brass to move forward when the firing pin strikes? When I think about what holds the brass against the bolt face, would it not be the extractor? The extractor holds the rim of the brass and would keep the brass from moving forward when fired, regardless of the headspace or the bullet seating depth, correct? That said, I am skeptical that either your over sized brass or your bullet seating depth have anything to do with your light primer strikes. The first two places I would look if I were having light primer strikes are my trigger and my primer seating. Looks like you have a TT trigger and those are generally rock solid but it would still be worth investigating to ensure everything is working properly with it. How did you seat the primers? Are you certain they are all the way bottomed out? And what brand are they? I have some rem primers for example that you can physically see the anvil protruding above the base of the cup, by probably 10-15 thousandths, I have to seat those very well to make sure that anvil gets pushed up into the cup.
On another note, you can be 100% sure of your exact seating depth from the lands. Check this video out, he describes the Hornady OAL tool, but then describes a much better method starting around 2:46, so I'd fast forward and start at that point.
I used this exact method on my 7SST just a few days ago. Once I got to where the bolt would close, I seated the bullet 1 thousandth deeper at a time until that "pop" on the bolt lift was gone completely, and called that my at lands depth, then I took a CBTO measurement and recorded that for future reference. I am going to start with my bullets 10 thousandths behind the lands. I would not recommend being right at the lands but I know some guys do.
On another note, you can be 100% sure of your exact seating depth from the lands. Check this video out, he describes the Hornady OAL tool, but then describes a much better method starting around 2:46, so I'd fast forward and start at that point.
I used this exact method on my 7SST just a few days ago. Once I got to where the bolt would close, I seated the bullet 1 thousandth deeper at a time until that "pop" on the bolt lift was gone completely, and called that my at lands depth, then I took a CBTO measurement and recorded that for future reference. I am going to start with my bullets 10 thousandths behind the lands. I would not recommend being right at the lands but I know some guys do.
archangel485
Well-Known Member
On another note, I heard from Forster yesterday, they let me know my die was on it's way back, they took very good care of me from a customer service perspective. Looking forward to getting the die (and my brass) back and taking some runout measurements with the new configuration. I suspect I'll be very satisfied with the results and will proceed to resize the remainder of my brass, but time will tell. Once I get my ladder test complete I'll run a few 5 shot groups for ES/SD verification and ensure it's grouping well, I will tune with the brake and seating depth if I need to. I'm getting excited, I've been shooting 6mm and 6.5mm stuff mostly for the last couple of years, I forgot how much I enjoyed the "big" stuff! 
SteelBanger
Well-Known Member
Take the following with a large grain of salt because I'm in no position to do any educating on this subject! lol My rifle shooting and loading background is 100% with gas guns up until this rifle build so this is my first experience dealing with loading for a bolt gun and I will simply try to explain what I did based on my conversations with my gun smith and others in this community.
When I first received my brass and sized them (luckily only the first 50) it took a ton of force to close the bolt on that empty brass. I started slowly bumping the shoulder back to the point I could close the bolt without interference but ended up going to far. That excess shoulder bump, even though it's only a few thousands of an inch allows the case to slightly move forward in the chamber and absorb the energy from the firing pin dropping on the primer, hence the light primer strikes. The thought behind pushing the bullet out into the lands is that will prevent the case from being able to move forward in the chamber which will let the primer take the full force of the firing pin and go bang. I had sent my barreled action back to my smith and he did this very thing and successfully fired one of the rounds I had sent with the rifle.
I don't have a modified case yet to thread onto my Hornady case gauge tool so the first time I pushed the bullets out I did it by feel similar to that video you posted, but I didn't have everything quite right. This last time I did it I found that bolt drop method on a different video (same exact process though) and used that to determine my seating depth at the lands so this time I should be good, and they should go bang ... in theory.
When I first received my brass and sized them (luckily only the first 50) it took a ton of force to close the bolt on that empty brass. I started slowly bumping the shoulder back to the point I could close the bolt without interference but ended up going to far. That excess shoulder bump, even though it's only a few thousands of an inch allows the case to slightly move forward in the chamber and absorb the energy from the firing pin dropping on the primer, hence the light primer strikes. The thought behind pushing the bullet out into the lands is that will prevent the case from being able to move forward in the chamber which will let the primer take the full force of the firing pin and go bang. I had sent my barreled action back to my smith and he did this very thing and successfully fired one of the rounds I had sent with the rifle.
I don't have a modified case yet to thread onto my Hornady case gauge tool so the first time I pushed the bullets out I did it by feel similar to that video you posted, but I didn't have everything quite right. This last time I did it I found that bolt drop method on a different video (same exact process though) and used that to determine my seating depth at the lands so this time I should be good, and they should go bang ... in theory.
SteelBanger
Well-Known Member
Glad to hear your die is on its way back, looking forward to seeing your results! Keep me posted.
archangel485
Well-Known Member
haha, okay fair enough. Like I said I'm learning too, and I've simply never heard of brass shoulders being bumped back so far that the firing pin couldn't ignite the primer, so that's a new one on me. I guess the extractor doesn't necessarily hold the brass tight enough to the bolt face, which surprises me a little, just because it seems like the firing pin drives into the primer much deeper than the piece of brass can move back and forth when it's in the bolt, but apparently it can.
Rardoin
Well-Known Member
Correct....there is enough 'play' between the extractor lip and the rim to allow forward movement of undersized brass. For this reason Ackley Improved chambers are designed to be cut about 0.004" short of the case head to neck/shoulder junction so that area binds upon chambering a parent case and forces the case head against the bolt face. Hard jamming the bullet is another way of accomplishing the same task as is making a false shoulder on some cases (such as the Dasher). Either way, during fireforming, regularly grease the lugs to reduce the chance of galling. I re-grease every 15rds or so when forming forming cases that have increased shoulder angles....such as the 7SS.
archangel485
Well-Known Member
Well things are moving along pretty quickly and easily for me. I worked up a ladder test, found 2 nodes and went with the higher node. I loaded up a 5 shot group and got an ES of 11, SD of 4.7, and didn't have to do a thing to the brake or seating depth to get it to group well, see attached, so that will save me a bunch of time and components etc. I'm going to work on getting the rest of my brass cleaned up and sized, then I'll start shooting it at distance to see what happens. Forgive the target, it's what I had. I couldn't be more satisfied with my results.
