.308 Overall Length Varation with 175gr SMK

[reloadingnoob]

Hello everyone,
I am currently working on loading .308 with 175gr Sierra Match King bullets on a Dillon RL550C and Dillon's .308 dies.

I am noticing that my OAL after seating is varying and I suspect it may be related to the imperfections at the tip of every SMK bullet influencing this. My goal OAL is 2.800in, however I am getting the following lengths on the last 5 test runs:

2.799
2.806
2.789
2.800
2.805

I understand that a variation if +/- .005in should be expected for OAL, however I do notice that the measurement can change with where I decide to measure from the tip of the bullet the tips are often slanted with high points and lower points.

So in essence I have 3 questions:
1. Is this bullet tip variation and OAL variation something I need to worry about, or should I accept this range and be satisfied so long as the average is around 2.800?
2. I am not crimping since this will be going into a magazine fed bolt action rifle and my understanding is it won't be necessary in this use case - do you crimp in your mag fed bolt actions?
3. The completed cartridge does not fit into the case gauge post-seating without a crimp however will fit in my chamber fine. This is to be expected right?

Thanks in advance!

 

[918v]

Are you able to measure the seating depth off the ogjive? Some of the variance can come from inconsistent neck tension or seating effort or slop the press itself.

 

[reloadingnoob]

Not at the moment, I will need to purchase a tool do do this however the manuals typically give an OAL recommendation and does not give a recommendadtion for powder charge + ogive to base length for each specific load. How would you go about this if going strictly off the manual?

 

[sinister]

Match bullets gain consistency (over other styles) by being base-drawn, making for uniform bases and boat-tails.

Long-range shooters and manufacturers will crimp and trim (true) hollow point tips. Shooters will gain consistency at the cost of a slight windage loss. Most will not see a difference at 300 yards and closer.

 

[straightshooter1]

Hello everyone,
I am currently working on loading .308 with 175gr Sierra Match King bullets on a Dillon RL550C and Dillon's .308 dies.

I am noticing that my OAL after seating is varying and I suspect it may be related to the imperfections at the tip of every SMK bullet influencing this. My goal OAL is 2.800in, however I am getting the following lengths on the last 5 test runs:

2.799
2.806
2.789
2.800
2.805

I understand that a variation if +/- .005in should be expected for OAL, however I do notice that the measurement can change with where I decide to measure from the tip of the bullet the tips are often slanted with high points and lower points.

So in essence I have 3 questions:
1. Is this bullet tip variation and OAL variation something I need to worry about, or should I accept this range and be satisfied so long as the average is around 2.800?

That variation in bullet OAL's in what I'd call "normal" with a lot of SMK's. As mentioned by 918v above, variation in your seating can easily come from a any one or a combinations of inconsistent neck tension, slop in your press and interference from the surface of the necks. To see your seating differences, it better to measure your CBTO's as SMK's can have less variance in their BTO's than their OAL's.

If you really want good uniform cartridges, you may need to think about going with an arbor press and seating die like an L.E. Wilson seating die.

2. I am not crimping since this will be going into a magazine fed bolt action rifle and my understanding is it won't be necessary in this use case - do you crimp in your mag fed bolt actions?

You're right. . . for a bolt fed action there's really no need for crimping. Just find the right "neck tension" that works for you.

3. The completed cartridge does not fit into the case gauge post-seating without a crimp however will fit in my chamber fine. This is to be expected right?

Thanks in advance!

Did you check the cases with the case gauge before seating? Sounds like something isn't quite right with the sizing process. . . like maybe the mouths are being faired???

If they fid your chamber fine, you should be ok. But, I'd do some checking to see what's going on with the case prep.

PS: If you try some 169 or 177 SMK's, I find they have more consistent OAL's than other SMK's as they've been factory pointed.

 

[E_T_G]

Are you using a powder drop on the Dillion? If so the variations in powder charges will have a much greater effect on accuracy than a few thousandths OAL.

 

[reloadingnoob]

That variation in bullet OAL's in what I'd call "normal" with a lot of SMK's. As mentioned by 918v above, variation in your seating can easily come from a any one or a combinations of inconsistent neck tension, slop in your press and interference from the surface of the necks. To see your seating differences, it better to measure your CBTO's as SMK's can have less variance in their BTO's than their OAL's.

If you really want good uniform cartridges, you may need to think about going with an arbor press and seating die like an L.E. Wilson seating die.


You're right. . . for a bolt fed action there's really no need for crimping. Just find the right "neck tension" that works for you.


Did you check the cases with the case gauge before seating? Sounds like something isn't quite right with the sizing process. . . like maybe the mouths are being faired???

If they fid your chamber fine, you should be ok. But, I'd do some checking to see what's going on with the case prep.

PS: If you try some 169 or 177 SMK's, I find they have more consistent OAL's than other SMK's as they've been factory pointed.

Thanks for the reply, yes it seems my SMK's look very similar to the 2nd before and after imaging Sinister had posted. I think this is likely the cause for this variance in COAL. Interestingly I measured the COAL of a pack of 175gr Federal GM SMK and the lengths varied from 2.799-2.803.

I almost wonder if flattening the tips of each SMK bullet would be a good idea haha.

My cases fit perfectly in the case gauge after sizing/prior to seating. It is only after seating that it no longer fits all the way in the case gauge - wasn't sure if this is a normal occurrence since it has not yet been crimped?

 

[reloadingnoob]

Match bullets gain consistency (over other styles) by being base-drawn, making for uniform bases and boat-tails.

Long-range shooters and manufacturers will crimp and trim (true) hollow point tips. Shooters will gain consistency at the cost of a slight windage loss. Most will not see a difference at 300 yards and closer.

Thanks for sharing this, the SMKs I purchased look very similar to the 2nd picture showing an angled/slanted tip/meplat. How do people usually go about this - do they flatten the tip or is it just easier to measure the CBTO on a perfect cartridge with 2.800 COAL and base it off of that?

I did read about finding the lands on your specific chamber and determining the CBTO based on that for maximum accuracy however I'm still watching videos at this time to learn about how to do that.

 

[chd]

Given what @E_T_G said, if you do take data off of your powder charges we'd probably all be interested in hearing about it.

 

[wvfarrier]

Are your cases annealed? If not, you could be getting some creep.

 

[straightshooter1]

Thanks for the reply, yes it seems my SMK's look very similar to the 2nd before and after imaging Sinister had posted. I think this is likely the cause for this variance in COAL. Interestingly I measured the COAL of a pack of 175gr Federal GM SMK and the lengths varied from 2.799-2.803.

I almost wonder if flattening the tips of each SMK bullet would be a good idea haha.

My cases fit perfectly in the case gauge after sizing/prior to seating. It is only after seating that it no longer fits all the way in the case gauge - wasn't sure if this is a normal occurrence since it has not yet been crimped?

My loaded cartridges fit nicely into my case gauge and I've never had that issue.

Something is happening with your Dillon and its dies that shouldn't be happening. I'd be taking measurements at every step to isolate exactly where this issue happens, which sounds to me like something having to do with the seater die in the Dillon. You can experiment with a different die and or process for seating to see if you come up with a different result.

BTW: what brass is it your having this problem with?

"Flattening the tips" is kinda what pointing bullets is about . . . mainly to improve BC consistency from bullet to bullet in addition to improving BC all together. It's a lot of work (sorting, trimming, pointing) to get good performance for extreme long distance shooting. Interestingly, if you look at Hornady A-Tip bullets, you'll see the tip is actually flat and small and they do that by design having found that feature actually improves the bullet's BC. Unless you're dong ELR shooting, there's really no need to think about "flattening the tips" .

 

[riverside jeep]

Had the same problem with the same projectiles, also with the 168 SMK. I contacted RCBS and sent them 3 bullets of each, they machined seating plugs for each for cheap ( I thought) and problem solved.

 

[Baron23]

Hello everyone,
I am currently working on loading .308 with 175gr Sierra Match King bullets on a Dillon RL550C and Dillon's .308 dies.

I am noticing that my OAL after seating is varying and I suspect it may be related to the imperfections at the tip of every SMK bullet influencing this. My goal OAL is 2.800in, however I am getting the following lengths on the last 5 test runs:

2.799
2.806
2.789
2.800
2.805

I understand that a variation if +/- .005in should be expected for OAL, however I do notice that the measurement can change with where I decide to measure from the tip of the bullet the tips are often slanted with high points and lower points.

So in essence I have 3 questions:
1. Is this bullet tip variation and OAL variation something I need to worry about, or should I accept this range and be satisfied so long as the average is around 2.800?
2. I am not crimping since this will be going into a magazine fed bolt action rifle and my understanding is it won't be necessary in this use case - do you crimp in your mag fed bolt actions?
3. The completed cartridge does not fit into the case gauge post-seating without a crimp however will fit in my chamber fine. This is to be expected right?

Thanks in advance!

IMO opinion those magnitude of differences can be easily attributed to the meplat (tip of the bullet, yeah) inconsistency in the cup pulled over the lead core. This shown pretty clearly in the pics posted above.

Except for issues of fitting inside mag length, who cares. The key to performance is CTBO (measure to the ogive which is what die in your press is actually set up for) so do get a bullet comparator and good caliper (if you don't have one already).

If you really, really, really want you can get a bullet tip trimmer but now you'd be jumping into the rabbit hole of bench rest and F-open folks. Up to you....I don't think you will find any benefit unless you shoot one of those types of very high precision games.

bullet tipping trimmer - Google Search

 

[sinister]

How do people usually go about this - do they flatten the tip or is it just easier to measure the CBTO on a perfect cartridge with 2.800 COAL and base it off of that?

Bullet Pointing Die System - Whidden Gunworks

Order Now! A great article on pointing bullets. Bullet Pointing Die System A bullet pointing die is a die used to make a sharper point on a bullet. By

www.whiddengunworks.com

 

[E_T_G]

reloadingnoob, are you running a compressed load? If so, that could be the case guage issue. What brass? Military brass has less volume. You never gave the brand of case or powder and charge.​

 

[reloadingnoob]

reloadingnoob, are you running a compressed load? If so, that could be the case guage issue. What brass? Military brass has less volume. You never gave the brand of case or powder and charge.​

Hi, thus far I have not yet added powder, just adjusting my dies for seating length - brass is a mix of PPU and Norma - I plan to use IMR 4064 however am only test seating at this time.

 

[Doom]

So in essence I have 3 questions:
1. Is this bullet tip variation and OAL variation something I need to worry about, or should I accept this range and be satisfied so long as the average is around 2.800?
2. I am not crimping since this will be going into a magazine fed bolt action rifle and my understanding is it won't be necessary in this use case - do you crimp in your mag fed bolt actions?
3. The completed cartridge does not fit into the case gauge post-seating without a crimp however will fit in my chamber fine. This is to be expected right?

In relation to #1. The interface between the cartridge, bullet and the chamber is what matters. In the case of the bullet to achieve uniform dimensions from round to round the dimension that matters is the beginning of the bullet bearing surface with the beginning of the lands. This is where the bullet diameter and the bore first make contact. Your seating die does not use the tip when seating but uses the diameter of the bullet near/at the bearing surface to achieve uniformity in the "base to ogive" dimension. Ogive in this case meaning the beginning of the reduction of the bearing surface. The ogive (bearing surface to tip) is never in contact with the rifle. The only reason that the COAL is included in the SAAMI specification is for the ammunition to be usable it must be able to fit in the rifle's magazine.

In relation to #2. It is not necessary to crimp in bolt action rifles and is not typically done in target rounds. However, hunting rounds may be crimped since they may be loaded multiple times before firing and may be used in heavy recoiling rifles multiple times before being fired.

In relation to #3. Not knowing what sizing die you are using I am puzzled by this. If in fact this is corrected by crimping it implied that the neck mouth is flared which as far as I know is only done with newer Lee Collet neck sizing dies or your case necks are too thick. However if the rifle chambers the round and a bullet will easily enter the neck of a fired round you are OK.

 

[straightshooter1]

In relation to #1. The interface between the cartridge, bullet and the chamber is what matters. In the case of the bullet to achieve uniform dimensions from round to round the dimension that matters is the beginning of the bullet bearing surface with the beginning of the lands. This is where the bullet diameter and the bore first make contact. Your seating die does not use the tip when seating but uses the diameter of the bullet near/at the bearing surface to achieve uniformity in the "base to ogive" dimension. Ogive in this case meaning the beginning of the reduction of the bearing surface. The ogive (bearing surface to tip) is never in contact with the rifle. The only reason that the COAL is included in the SAAMI specification is for the ammunition to be usable it must be able to fit in the rifle's magazine.

In relation to #2. It is not necessary to crimp in bolt action rifles and is not typically done in target rounds. However, hunting rounds may be crimped since they may be loaded multiple times before firing and may be used in heavy recoiling rifles multiple times before being fired.

In relation to #3. Not knowing what sizing die you are using I am puzzled by this. If in fact this is corrected by crimping it implied that the neck mouth is flared which as far as I know is only done with newer Lee Collet neck sizing dies or your case necks are too thick. However if the rifle chambers the round and a bullet will easily enter the neck of a fired round you are OK.

I don't know of any seating dies that are able to make contact at or near the bearing surface. That would be ideal, if it could be done.

Because my seating stems make contact very high on the ogive, that's exactly why I sort my bullet with a comparator that makes contact at the same place as my seating stems, to help produce the most consistent seating depths (being that there's some variation between the contact point of a standard comparator and the contact point of a seating stem).

 

[Baron23]

I don't know of any seating dies that are able to make contact at or near the bearing surface. That would be ideal, if it could be done.

Because my seating stems make contact very high on the ogive, that's exactly why I sort my bullet with a comparator that makes contact at the same place as my seating stems, to help produce the most consistent seating depths (being that there's some variation between the contact point of a standard comparator and the contact point of a seating stem).

View attachment 8592577

Ah, maybe try a VLD stem?

 

[straightshooter1]

Ah, maybe try a VLD stem?

VLD stems don't go very far down the ogive either.

 

[Doom]

I don't know of any seating dies that are able to make contact at or near the bearing surface. That would be ideal, if it could be done.

Because my seating stems make contact very high on the ogive, that's exactly why I sort my bullet with a comparator that makes contact at the same place as my seating stems, to help produce the most consistent seating depths (being that there's some variation between the contact point of a standard comparator and the contact point of a seating stem).

View attachment 8592577

Right you are! It had been a short night. Thanks for keeping an eye on me.