I picked up a couple of boxes of 300 WSM Custom Brass the other day. When working up my initial COAL, I tried an unprimed round just to see how it would feed. The bolt would not close all the way. This is on a Tikka T3. I pulled the projectile off and tried again, still no luck. I used a Hornady Lock-N-Load® Headspace Comparator and measured the length from the cartridge face to the datum line and it was about 1.747 - 1.746 on about all 10 cases that I measured. SAAMI has it at 1.7260+.0005, and my Modern Reloading 2nd Ed. Richard Lee manual has it at 1.730. I shoulder bumped a case down to 1.7415 and then the bolt closed, but still tight. Did I get a bad batch, or what is the datum line from the factory supposed to be? Anyone have a factory round or brass that they could measure to compare?
Shoulder Bump for New 300 WSM Nosler Custom Brass
- Thread starter gonfad
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mjcmichigan
Handloader
- Dec 26, 2016
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Right or wrong,
New brass I do Full length size atleast to a known measurement. SAAMI or previously fired brass.
If I don’t have fired brass… I did this in February.
Back in February, had new 22-250 cases.
Procedurally I full length sized 5 cases.
Starting loads, fired the 5, reloaded them again and slowly worked up to full loads.
Each time I measured the cases. They didn’t all reach full chamber size at the same time. I think it was 5 reloads before they all got to the same size. Probably from starting loads, and maybe differences in individual pieces of brass?
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New brass I do Full length size atleast to a known measurement. SAAMI or previously fired brass.
If I don’t have fired brass… I did this in February.
Back in February, had new 22-250 cases.
Procedurally I full length sized 5 cases.
Starting loads, fired the 5, reloaded them again and slowly worked up to full loads.
Each time I measured the cases. They didn’t all reach full chamber size at the same time. I think it was 5 reloads before they all got to the same size. Probably from starting loads, and maybe differences in individual pieces of brass?
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using the hornady tool "E" insert 0.420" . I measure 1.740"
if I was in your shoes , I'd just keep bumping the shoulder back a couple thousandths at a time until the bolt closes with light resistance .by doing this it should help gain brass life . there is no reason to push them way back then let them grow back .
if I was in your shoes , I'd just keep bumping the shoulder back a couple thousandths at a time until the bolt closes with light resistance .by doing this it should help gain brass life . there is no reason to push them way back then let them grow back .
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I have some 308 Winchester and 270 Winchester Nosler Custom/Premium brass as well, so I measured those as a sanity check. Both were well under SAAMI spec out of the box. Also checked some Nosler Trophy factory cartridges in 308 Win. and 300 Win Mag. Both were also under SAAMI too. My RCBS die with the RCBS shell holder doesn’t look like it’s going to give me more than 1.7415. Could be that my gauge is reading incorrectly, but if this is supposed to be ready to load brass, I would expect it to be similar to the others and be under spec. I understand the logic behind FL sizing every time, but that should be an optional with brass that is advertised as ready to load.
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In my opinion Jim has got it right, although if it's that tight you might end up doing like Mjcmichigan and just full length resize them. That's why I asked if you had any other fired cases to go off of.
If it's really bad you might have to do as Coop22250 done and get a die to bump the shoulder back harder.
Beyond that I feel like there is some numbers being thrown around that should be cleared up. The Saami spec measurements to the datum line are irrelevant and should be thrown out of the discussion.
I don't own one, but your Hornady gauge does NOT measure Saami spec to the case datum line. It's simply a way to precisely measure from the base to the shoulder of a fired case, which then lets you set your die to bump .00X to set headspace as you see fit. Hence the name comparator. It lets you compare.
Or to see the difference from new brass, to when it's fired in your chamber. You mentioned 270 and 308 new brass being WELL under Saami spec. After firing it will likely still be under spec by your measurements because it will only grow by a couple .000. The measurement is just a number to give you that number to go off of. Not a Saami spec number to the exact datum line. Make sense?
I have a tool that I made. My measurement would guaranteed be different than yours on a 300 WSM, because it will sit either somewhat long or short on the slope of the shoulder compared to your tool. What that number is doesn't matter. As long as I have a number, I can set the die to bump just as precisely.
Being that your measurement is already way over, you will not get anywhere close to the Saami spec of 1.730 and shouldn't try unless you want major problems on first firing. That's not the measurement your Hornady tool is making, nor intended for.
If it's really bad you might have to do as Coop22250 done and get a die to bump the shoulder back harder.
Beyond that I feel like there is some numbers being thrown around that should be cleared up. The Saami spec measurements to the datum line are irrelevant and should be thrown out of the discussion.
I don't own one, but your Hornady gauge does NOT measure Saami spec to the case datum line. It's simply a way to precisely measure from the base to the shoulder of a fired case, which then lets you set your die to bump .00X to set headspace as you see fit. Hence the name comparator. It lets you compare.
Or to see the difference from new brass, to when it's fired in your chamber. You mentioned 270 and 308 new brass being WELL under Saami spec. After firing it will likely still be under spec by your measurements because it will only grow by a couple .000. The measurement is just a number to give you that number to go off of. Not a Saami spec number to the exact datum line. Make sense?
I have a tool that I made. My measurement would guaranteed be different than yours on a 300 WSM, because it will sit either somewhat long or short on the slope of the shoulder compared to your tool. What that number is doesn't matter. As long as I have a number, I can set the die to bump just as precisely.
Being that your measurement is already way over, you will not get anywhere close to the Saami spec of 1.730 and shouldn't try unless you want major problems on first firing. That's not the measurement your Hornady tool is making, nor intended for.
SAAMI calls out headspace on 300wsm at 1.7260-1.7360:
I have no idea what your tool measures, I don’t own one either. Seems silly to sell something to measure headspace with that doesn’t measure headspace[emoji3]. 1.730 is within range according to SAAMI. Bumping your new cases back a little at a time until they fit is a good suggestion. Then take a fired case and set back .002-.003 with your measuring device that doesn’t read true headspace. Haha.
I have no idea what your tool measures, I don’t own one either. Seems silly to sell something to measure headspace with that doesn’t measure headspace[emoji3]. 1.730 is within range according to SAAMI. Bumping your new cases back a little at a time until they fit is a good suggestion. Then take a fired case and set back .002-.003 with your measuring device that doesn’t read true headspace. Haha.
GB, the Hornady headspace comparator gauge allows for headspace comparison between fire formed brass and resized brass, as stated by Hornady themselves.
It is not a go/no-go gauge, nor is it intended to be.
The 0.420 bushing recommended by Hornady is for 19 different cartridges varying in shoulder diameter and angle. Not to mention any variation in the bushings themselves between one tool kit and another.
Depending on the specific cartridge it's being used on it may very well measure out within saami specs every time. But it can just as easily not.
You proved my point with your above post. Saami max chamber spec is 1.736. The O.P has a measurement of 1.747. Jim has a measurement of 1.740 on his brass. How do you explain that??
The O.P stated that sized down to 1.7415 by his measurement it closes but is tight, so we know he's getting real close. Lets say sized down to 1.738 by his measurement it closes fine and after firing it measures 1.740. You think his new Tikka is .004 past max saami chamber allowance? Has to be. Can't be the Hornady tool that is sold as a "comparator."
I mean that thing is an official Saami chamber measuring gauge. I'd bank on it.
It is not a go/no-go gauge, nor is it intended to be.
The 0.420 bushing recommended by Hornady is for 19 different cartridges varying in shoulder diameter and angle. Not to mention any variation in the bushings themselves between one tool kit and another.
Depending on the specific cartridge it's being used on it may very well measure out within saami specs every time. But it can just as easily not.
You proved my point with your above post. Saami max chamber spec is 1.736. The O.P has a measurement of 1.747. Jim has a measurement of 1.740 on his brass. How do you explain that??
The O.P stated that sized down to 1.7415 by his measurement it closes but is tight, so we know he's getting real close. Lets say sized down to 1.738 by his measurement it closes fine and after firing it measures 1.740. You think his new Tikka is .004 past max saami chamber allowance? Has to be. Can't be the Hornady tool that is sold as a "comparator."
I mean that thing is an official Saami chamber measuring gauge. I'd bank on it.
TackDriver284
Handloader
- Feb 13, 2016
- 2,524
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I would just keep bumping back the shoulders back a little at a time until the bolt closes easier and set the die and size all the new brass until the next firing. After the next firing, i would measure the headspace on 5 fired cases, try each one of them in the rifle again and see if the bolt closes fine, if it does, then measure the fired case headspace, and keep note of it, then size the first fired case using that die you used on the new brass and see what headspace measurement you got after sizing, if it's bumped .002" less after sizing, then leave the sizing die alone and try the sized brass again in your rifle and see how the bolt closes. If its not .002" less, then re-adjust the die until you get .002" shoulder bump, once you get to that point, set the die and size 5 more pieces and try them in your rifle, if its good, then you are good to size the rest of them.
I’d be surprised if his tikka is out of spec. I guess stranger things have happened though. Odd to get new brass so long. I’ve never experienced that. Most of the stuff I get is short. Had some Hornady that was .020 short. That’s not measured with a “comparator” but with a stub gauge made with the chamber reamer.ShadeTree":2b8qaufe said:
Thanks for the explanation by the way.
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gbflyer":2276h0a6 said:
Delving into things and hammering out discussions is how we all can figure things out. I could be wrong, but so far just going off of numbers stated.
We don't know that the brass is long, only long for his chamber. It could very well be long and way out of spec. Or he could have a minimally spec'd chamber and max spec'd brass. We'd only know for sure if we were starting out with a definitive number. Such as your stub chamber gauge you mentioned.
Jim didn't state his brass was long, or long for his chamber. Only that it measures 1.740 with the Hornady tool using the 0.420 bushing.
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- #17
Just ran into this last night in a .223. Once fired case measured 1.480 and virgin LC 5.56 brass measured 60% @ 1.480. The other 40% were .001-.003" over and need the shoulder bumped right out of the gate. As stated above, it's a comparator not a headspace gauge. You could however use the comparator on a headspace gauge if you wanted. I feel that measuring and comparing off of fired brass is good for me.
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- #19
Quick update on the measurements. Thank you to those pointing out that it’s a comparator, and not for measuring headspace. I missed the fact that the bushing is at 0.420 and the datum line in SAAMI is at 0.4450. That means with the 35 degree angle, my point of measure (roughly) would have been about 0.017677 long, so out of the box the case were 1.7283-1.7293 and I was bumping to 1.7238. Again, this is still not a precise measurement because the comparator bushing might not be right on 0.420. If this is close, it looks like everything might be in spec and the chamber is just on the short end of the spec and the cases on the long end.
Cheers!
*Edit on my math. Not good with triangles, so the method to get 0.017677 wasn't precise. For more precise math, subtract diameter of bushing from diameter of datum line 0.445 - 0.420 = 0.0245. Divide by 2 to because the triangle will be only one side of the cartridge = 0.0125. Calculate triangle using height of 0.0125 and angle of 35 degrees = base of 0.017852. Out of the box the case were 1.728148 - 1.729148 & bumping to 1.723648.
Cheers!
*Edit on my math. Not good with triangles, so the method to get 0.017677 wasn't precise. For more precise math, subtract diameter of bushing from diameter of datum line 0.445 - 0.420 = 0.0245. Divide by 2 to because the triangle will be only one side of the cartridge = 0.0125. Calculate triangle using height of 0.0125 and angle of 35 degrees = base of 0.017852. Out of the box the case were 1.728148 - 1.729148 & bumping to 1.723648.
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- #20
Got the rifle back and chamber is good. The fired case from the gunsmith measures 1.740 on the comparator. So I guess that settles it. The chamber is just tight and new cases will need to be bumped backed a bit to fit if they don’t out if the box. Thanks again to all who provided insight.
