Throating to avoid neck/shoulder junction

[Kratos]

This may be a stupid question, but when you are determining throat length to accommodate a given seating depth for a bullet, how do you decide where to put it? Do you just eyeball it? Do you do the calculations and then give it 0.020" margin of safety?

 

[jackieschmidt]

As you might have discovered, using a throater can be a tad tricky.

What I do is take a new case that slips into the chamber with no resistance, and, using a heavy neck tension, seat a bullet where I want it to be in the neck. The straighter the round, the better.

I then run the throater in a little at a time until the case head-spaces correctly.

You have to be careful not to overshoot. I have my own home made device that allows me to keep track of just how far I am going in.

The key to using a throater is getting the next barrel to be as close to the previous one as possible.

Many of the reamer manufacturers make devices that allow you to keep track of just where you are with the throater.

this is a neat one by Pacific
http://pacifictoolandgauge.com/throat-and-neck-reamers/5226-17-cal-uni-throater-kit.html

 

[Kratos]

As you might have discovered, using a throater can be a tad tricky.

What I do is take a new case that slips into the chamber with no resistance, and, using a heavy neck tension, seat a bullet where I want it to be in the neck. The straighter the round, the better.

I then run the throater in a little at a time until the case head-spaces correctly.

You have to be careful not to overshoot. I have my own home made device that allows me to keep track of just how far I am going in.

The key to using a throater is getting the next barrel to be as close to the previous one as possible.

Many of the reamer manufacturers make devices that allow you to keep track of just where you are with the throater.

Yes, the locking nut with the PT&G unithroater seemed to work well, such that I was able to advance the throat about 0.050. But my question is more about the dummy round—how do I decide how deeply to seat the bullet and still avoid the neck/shoulder junction? Is there a better way to measure than just holding a bullet next to the case and eyeballing it?

 

[geraldgee]

With a Dremel (or whatever you have on hand), you can cut a window into your neck from the case mouth to the shoulder juncture wide enough that you can visually verify exactly where the bearing surface of your bullet ends and the boat tail begins. You can make your determination much easier when you can see it.
Good luck with it.

 

[swd]

I use a split case like Gearld. I like the boat tail junction to be about 1/3 up from the shoulder and half way is fine if your really trying to maximize capacity. If your mag feeding you'll have to take that length into consideration.

 

[jackieschmidt]

Yes, the locking nut with the PT&G unithroater seemed to work well, such that I was able to advance the throat about 0.050. But my question is more about the dummy round—how do I decide how deeply to seat the bullet and still avoid the neck/shoulder junction? Is there a better way to measure than just holding a bullet next to the case and eyeballing it?

I’m sure someone makes a tool that gives an ideal distance that the junction of the boat tail and bullet shank should be from where the donut forms, but I just eyeball it.

Here is a Bart’s 80 grain and where I like it to be.

 

[Will Henry]

I have always just held a bullet next to the dummy and felt OK with it. I generally allow about .050, depending on the cartridge. It is easy when the chambering reamer hasd no throat but is a little more difficult when extending a throat, depending on the diameter of the throater and the throat. It can be difficult to feel when the reamer first starts to cut and one is likely to cut a few thou before he realizes it. I don't really like extending throats because I am always concerned about diameters not matching up so there is a step (though minor) in the throat. Probably a little OCD on my part.
When it come to avoiding the neck/shoulder juncture, the benefits of cartridges with a longer neck, are readily apparent. My 30/40 gives me a lot of latitude! WH

 

[Kratos]

Unfortunately this is a Dasher, so the short neck is limiting. I got this barrel before I knew much about chamber geometry, and didn’t even ask about the free bore, which turned out to be .104. This is way too short for the Berger 109s I’m planning to shoot. As it is, with the free bore extended .050, I can still only jump them about .040 before I run back into the shoulder, so I may end up extending it a bit more.

 

[Ned Ludd]

Yes, the locking nut with the PT&G unithroater seemed to work well, such that I was able to advance the throat about 0.050. But my question is more about the dummy round—how do I decide how deeply to seat the bullet and still avoid the neck/shoulder junction? Is there a better way to measure than just holding a bullet next to the case and eyeballing it?

There is no hard and fast rule about how much bullet bearing surface you have to have in the neck. As noted above, many just eyeball it. The human eye is more than capable of giving sufficient accuracy in terms of placing the bullet in the neck. I prefer to seat bullets with the boattail/bearing surface junction somewhere between one fourth and halfway out the neck (i.e. above the neck/shoulder junction). In many cartridges, seating the bullet with the boattail/bearing surface junction ~halfway out the neck will give approximately one half caliber of bullet bearing surface in the neck, which is plenty.

Quickload reloading software uses SAAMI case measurements to provide a numerical output of how deep in the neck a bullet will be seated at a given COAL. This is a nice feature to have and is useful when making estimates of how far a rifle needs to be throated out with a given bullet. However, there are caveats involved in the use of these outputs. First, their accuracy may be questionable depending on how your specific cases are sized with respect to SAAMI standards. I'd expect variance caused by this to generally be pretty small and not worth much concern.

Also, until the rifle has been throated out and seating depth optimized at the new charge weight and COAL, there is no way to be 100% positive exactly where a new load will tune in with respect to seating depth in relation to the lands. For example, let's say you previously had a well-tuned load with the bullet boattail/bearing surface junction very close to the case neck/shoulder junction (i.e. almost all the way down in the neck). In that load, let's also say you found the optimal seating depth was .020" off the lands. If you were to throat that rifle out by an additional .100" or so to move the bullet boattail/bearing surface junction farther out (i.e. closer to the middle of the neck), you have now changed several load parameters, such as increasing the effective internal case volume. A new load will require more powder to achieve the same velocity, and it will do so at slightly less pressure than was required previously. There is no guarantee that in the new load the bullet will still want to be seated at .020" off the lands in the new configuration. You can only know this with certainty by doing a seating depth test. The bullet might tune in at .020" off the lands in the new load, but it might easily tune in somewhere else.

So you can see how you might end up with a "chicken or the egg" scenario. For that reason, "eyeballing" the location of boattail/bearing surface junction is usually more than sufficient. In a cartridge with a neck length of approximately one caliber, if you keep the boattail/bearing surface junction somewhere from between about one fourth the way out the neck to no more than just under three fourths the way out the neck, you will have approximately half a caliber or slightly under in which to adjust seating depth. Likewise, if you take the more conservative route and keep the boattail/bearing surface junction between one fourth and halfway out the neck, you would have approximately one fourth caliber to play with in terms of seating depth adjustment. For example, that would mean a useful seating depth test range of almost .060" for a .224" bullet, and almost .080" for a .308" bullet, which is usually sufficient. Although there might possibly be a scenario with a certain bullet where this range could be problematic, it works quite well in the vast majority of instances and is why "eyeballing" the boattail/bearing surface junction is usually sufficient.

 

[Kratos]

Yes, it’s an optimization problem. On the one hand, many have reported the newer hybrids shoot best with significant jump, often .070-.080. But if I tested that much jump now, the bullet would be seated deeply into the case—there shouldn’t be a donut on virgin or once fired brass, I think, but as stated above the combustion volume will be significantly smaller. But with the short dasher neck, if I moved the throat out that far, then I wouldn’t have much room to go back or use a bullet with a shorter nose or bearing surface.

 

[Ned Ludd]

Yes - it's always an arms race (no pun intended) if you want to keep up and test the latest bullet offerings. They almost always tend to get longer and heavier with time. I did not mention this in the previous post, but I have developed loads for several bullets with the boattail/bearing surface junction at, or even below, the case neck shoulder junction due to having insufficient freebore in a given rifle. They shot just fine, certainly well enough for me to decide I wanted the option of loading them more optimally, thus making the decision to extend the freebore. Nonetheless, that can be a hard choice to make if it means you will have to seat some other bullet that also works very well sub-optimally. Certainly having a bunch of barrels throated differently for different bullets would be one way to go about it. But that can be a relatively expensive and time-consuming approach. You might be able to decide on the best possible compromise freebore length to shoot several different bullets from the same barrel, especially if they're close to one another in terms of BTO. However, if they're quite different, it may necessitate a different barrel/freebore, or having to load them sub-optimally initially to determine whether they're worth the effort.

 

[243winxb]

avoid the neck/shoulder junction

If neck turning and using a bushing die that doesnt size all the way to the shoulder, whats the issue seating the bullet shank below the neck?

Donut, tight neck chamber, .003" clearance not enough? Just asking.

 

[Kratos]

If neck turning and using a bushing die that doesnt size all the way to the shoulder, whats the issue seating the bullet shank below the neck?

Donut, tight neck chamber, .003" clearance not enough? Just asking.

Fear of donut, I suppose. I may just plan to redo seating depth testing every time I get through a firing cycle on the brass. This is going to be mainly used for PRS so it’s probably not worth getting too far into the weeds, and the next barrel will be a BRA anyway.

 

[tsyarnall]

Fear of donut, I suppose. I may just plan to redo seating depth testing every time I get through a firing cycle on the brass. This is going to be mainly used for PRS so it’s probably not worth getting too far into the weeds, and the next barrel will be a BRA anyway.

Looking forward to reading your progress with a BRA barrel as I have great interest in it.

Scott

 

[Bottom Fodder]

Perfect timing on this thread! But trying not to highjack thank you Kratos for starting it
Researching for a next project (223 with heavy’s) option of sending a dummy round or self throating with Uni Throater
Which I could still Use/need a dummy round ( I prefer self throating)
I’ve read from min. Of 1/2 cal. Bearing
surface in neck to BT junction below neck shoulder junction. So if you were making a dummy round to use as a guide to cut free bore and to optimize case capacity were would you place the BT junction
In the case

 

[243winxb]

optimize case capacity were would you place the BT junction

No idea.

Hodgdon has the 90 gr hpbt at a COL of 2.380" If you look at all powders on the Hodgdon website, some have a "C" for compressed powder.
Why not start at this COL and make adjustments from there? Make the col longer, till powder is not compressed?

My factory bolt 223 rifle is 1.965" from bolt face to rifling. 9 twist shooting 69 gr Sierras. The magazine limits COL to 2.320"

80 & 90 gr @ 2.380" Making room in case for StaBALL 6.5 powder ??

 

[Ned Ludd]

Perfect timing on this thread! But trying not to highjack thank you Kratos for starting it
Researching for a next project (223 with heavy’s) option of sending a dummy round or self throating with Uni Throater
Which I could still Use/need a dummy round ( I prefer self throating)
I’ve read from min. Of 1/2 cal. Bearing
surface in neck to BT junction below neck shoulder junction. So if you were making a dummy round to use as a guide to cut free bore and to optimize case capacity were would you place the BT junction
In the case

Ideally, I'd want the bullet boattail/bearing surface junction between one fourth and halfway out the neck with the bullet at its optimal seating depth. That will give you very close to half a caliber of bearing surface in the neck, keep the bullet above any donut that might form, and maximize your useable case volume.

What "heavy" .224" bullets are you thinking of using? F-TR shooters using 80 to 90 gr bullets in the .223 Rem already have a pretty good handle on the freebores necessary for these bullets. If you do some searches here using "90 VLD", "85.5 Hybrid", or "80.5 Fullbore", you should find plenty of information.