7 PRC Sticky Bolt

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rmiked

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Nov 8, 2023
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#1
Shooting Seekins PH2 in 7 PRC. Loading once fired Hornady brass using Hornady dies. Load is 62.0 grains H4831SC at 3.300” COAL for 175 ELDX. The Hornady load data one below MAX is 62.4 grains at 3.265” COAL. My throat as measured using Hornady lock-n-load is 3.346”. So I’m 0.046” off lands. Rounds shoot great, 3 shot groups under 1/2”. For me and a
Hunting rifle I’m good with that. The bolt lift is sticky. The primers are not as flat as the last box of Hornady 175 ELDX I bought. You guys with experience, how much powder charge should I back off to alleviate a sticky bolt? I’m working up a hunting load. Rifle has 26” barrel. I’m good with 2850-2900 ft-sec as long as it’s repeatable. The factory stuff is not the same , lot to lot. I called Hornady and they said they were changing powders and charge trying to get back to the published 3000 Ft/sec. I’ll probably load the next group at 61.5 grains to see if dropping 1/2 grain fixes this.
 
#3
Ok. I’m at 62.0 grains. Since it groups well, I’ll drop down in 1/2 grain increments until the sticky bolt is gone. I hope I can still achieve a desirable velocity and not have a sticky bolt. I think 2850 fps would be fine if groups well. With a 26” barrel, should be doable. My case necks before shooting are 0.313” OD. After shooting they are 0.318”. The SAMMI chamber minimum dimension in 0.319”. So only 0.001” clearance if chamber reamer tight
 
#5
That’s true when the unfifred round is sitting in the chamber. But after firing it’s 0.001”. Doesn’t the sticky bolt come from the expanded case inside the chamber, after firing? I’m asking, not really sure. The base of the fired cartridge is 0.530” before and after firing, not really changing. The SAMMI chamber dimension at base is 0.533”. So I don’t see the base being the issue? I’m trimming the cases after resizing if needed. Perhaps the shoulder is moving forward slightly and that’s where the stick bolt comes from. Not sure. I thought a I read these PRC cartridges have tight chamber reamers and that makes them inherently more accurate. Maybe there is a trade-off with sticky bolts? Just thinking out loud.
 
#6
rmiked said:
That’s true when the unfifred round is sitting in the chamber. But after firing it’s 0.001”. Doesn’t the sticky bolt come from the expanded case inside the chamber, after firing?
Click to expand...

Yes. In every single case the clearance in the chamber after firing is .001”. It is clearance, the absence of interference. Even .0000001” of clearance after firing will release the case from the chamber without binding. What’s causing your hard bolt lift is the lack of clearance between the case head and the bolt face, not the .001” of clearance in the neck area.
 
#9
918v said:
Hornady brass is good.
Click to expand...


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#10
918v said:
Yes. In every single case the clearance in the chamber after firing is .001”. It is clearance, the absence of interference. Even .0000001” of clearance after firing will release the case from the chamber without binding. What’s causing your hard bolt lift is the lack of clearance between the case head and the bolt face, not the .001” of clearance in the neck area.
Click to expand...
Is that the end clearance between the bolt face and case head? If so is that caused by the brass stretching (getting longer) after firing? The Sammi case length is 2.280”. I’m trimming with a Lee trimmer to approx 2.270”.
 
#11
generally sticky bolt lift is associated with the diameter pushing into the chamber walls (this can be affected by the length but only if it is hard to close the bolt)

Brass not extracting or sticky bolt lift is either from too much pressure or the brass being too soft. Since you are under book max for pressure that leaves the brass.
 
#12
My Lee case trimmer states it trims 7 PRC to between 2.260”-2.280”. Mine is trimming to 2.275”. I ensured the case length gauge was inserted all the into the cutter. Not doing that trims long. I decided to shorten the length gauge 0.012”. Now it trims to 2.263”. That’s 12 thousandths extra clearance for case length before firing. Maybe that will unbind the case to bolt face dimension after firing. That along with reducing powder charge should get me moving in the right direction. If this doesn’t work I’ll try some ADG brass.
 
#13
rmiked said:
My Lee case trimmer states it trims 7 PRC to between 2.260”-2.280”. Mine is trimming to 2.275”. I ensured the case length gauge was inserted all the into the cutter. Not doing that trims long. I decided to shorten the length gauge 0.012”. Now it trims to 2.263”. That’s 12 thousandths extra clearance for case length before firing. Maybe that will unbind the case to bolt face dimension after firing. That along with reducing powder charge should get me moving in the right direction. If this doesn’t work I’ll try some ADG brass.
Click to expand...

Neck clearance isn’t the issue. If the round chambers without difficulty it’s not a dimensional spec issue
 
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#15
What reamer was used and what is the diameter at the base of cartridge for that reamer?

There's a known "issue" with PRC chambers. If you cut the chamber near the SAAMI minimum, it can be have a sticky bolt no matter what charge weight. Depending on the brass you're using and such.

Alex Wheeler is credited for figuring it out and having reamers spec'd on the high end of SAAMI and the problem goes away. It's usually labeled as an AW2 reamer or similar nomenclature.


If you do find out your chamber is near SAAMI minimum, all it takes is an AW2 reamer spun by hand in the chamber. Takes 5min or less and cleans up the base of the chamber.



Not saying this is your issue. Just something easy to check that will save you chasing your tail if that's the issue.
 
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#16
Rio Precision Gunworks said:
What reamer was used and what is the diameter at the base of cartridge for that reamer?

There's a known "issue" with PRC chambers. If you cut the chamber near the SAAMI minimum, it can be have a sticky bolt no matter what charge weight. Depending on the brass you're using and such.

Alex Wheeler is credited for figuring it out and having reamers spec'd on the high end of SAAMI and the problem goes away. It's usually labeled as an AW2 reamer or similar nomenclature.


If you do find out your chamber is near SAAMI minimum, all it takes is an AW2 reamer spun by hand in the chamber. Takes 5min or less and cleans up the base of the chamber.



Not saying this is your issue. Just something easy to check that will save you chasing your tail if that's the issue.
Click to expand...
The rifle is a Seekins PH2. If the chamber needs some work, I’ll let them do it. They have great customer service, I sure hope that’s not the case. I shot 2 boxes of Hornady 175 ELDX (same lot number ) with no issues. The 3rd box (different lot) started flattening and cratering primers and some slight sticky bolt lift. I called Hornady with the lot numbers and the 3rd box was a different powder mix and was faster velocity from their tests. That’s when I got some dies. Thanks for the heads up. I’ll know more after reducing powder charges and doing some more shooting.
 
#18
It was fired thru my rifle. And I am full length sizing. I can chamber the empty cases (with no bullet) thru the rifle without any sticky bolt. And these were rounds that were sticky to extract. It almost seems like a cooling issue. If I don’t attempt to extract immediately, it’s not as bad. But still sticky no matter how long I wait
 
#20
Well if I am full length sizing, therefore bumping shoulder , it has to be too high of pressure it seems. I have already loaded some lower charge . Will shoot soon.
 
#21
rmiked said:
It was fired thru my rifle.
Click to expand...
This narrows it down to pressure

rmiked said:
And I am full length sizing.
Click to expand...
Full-length sizing doesn't guarantee that you will size small enough. It depends on the relationship between the size of your chamber and the size of the die. Too big of a die, and you won't size enough (or at all) and that will eventually end up with a sticky bolt.

rmiked said:
I can chamber the empty cases (with no bullet) thru the rifle without any sticky bolt.
Click to expand...
But that won't necessarily stop a sticky bolt from happening with mismatched chambers/dies (see below).

rmiked said:
And these were rounds that were sticky to extract. It almost seems like a cooling issue. If I don’t attempt to extract immediately, it’s not as bad. But still sticky no matter how long I wait
Click to expand...

As the brass cools, it will contract slightly.

So, why, if you can chamber a case before you fire will it possibly end up with extraction difficulties?

Think about what happens with the rifle during a shot:

1) Ignition
2) Pressure builds
3) Case expands to the limits of the chamber - but it doesn't stop expanding... but how...?
4) The chamber expands slightly as well and the case keeps expanding too
5) The brass and chamber both spring back.

The chamber will spring back more quickly and will do so back to the original chamber size. The brass will not spring back to its original size. If the case is too close to the chamber size to begin with, then it won't spring back enough, and the chamber will essentially "grab" it, causing extraction issues. This is also caused by high pressure, which will cause the chamber (and thus the brass) to expand too much.

Regardless, it is likely that you are slightly over pressure.
 
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#23
Refer to post 15. Your chamber is too tight in the web. Rent a AW2 reamer from 4D reamer rentals and clean up the rear of the chamber by hand. The biggest cause for clickers/ sticky bolt is a tight chamber in the web/body diameter. Second is a die that doesn't size the brass body/web diameter enough. Third is pressure. Your load is still below book max. PRC is known for tight chambers. Saami chamber is only .001 clearance at the web. Should have been .0025-.003 instead for that family of cartridges.
 
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#24
When I had the issue with my Rem 700 bolt sticking and cases sticking everyone including “experts” said I need a small base die.

Fixed the known pre-extraction issue and the problem went away.

Contact Seekins. Their customer service could not be better. They’ll take care of this. Glenn will know what’s going on here……
 
#29
I did that (found clicking Utube) and watched a guy ream his chamber with an AW2 reamer. He removed his barrel from the action. And it cured the clicker issue and didn’t reduce accuracy. I don’t see removing a barrel with Seekins customer service. I sent an email to Seekins and hoping they already use the AW2 reamer. But the video made it seem like most PRC rifles could have an issue. Might depend on dies selected, brass used, etc. I have not had any clicking however, just sticky bolt lift.

I shot my rifle today with 1/2 grain reduction in powder charge (61.5 grains H4831SC) and no issues. I had also trimmed the brass another 0.012”. If the brass elongating was the issue , and not powder charge, I’m gonna try the higher powder charge with shorter brass and see if that was a contributor. The Sammi case length is 2.280” and my trimmer was only trimming to 2.275”. It’s easy enough to shorten the case length gage. I’m now at 2.263” which is still longer than the 2.260” minimum.

Will be interesting to see what Seekins says. I’m gonna order some ADG brass. Just wondering how much to reduce powder charge from book values since ADG claims their thicker brass and lower internal volume requires a reduction. Using Hornady brass and Hornady load data seems you can trust max data. Should probably drop a few grains and just test some out watching for pressure signs as you increase. Like everyone else, I just want reliable chambering, extraction and good groups. I’m not looking for speed records. Thanks
 
#33
rmiked said:
I shot my rifle today with 1/2 grain reduction in powder charge (61.5 grains H4831SC) and no issues. I had also trimmed the brass another 0.012”. If the brass elongating was the issue , and not powder charge, I’m gonna try the higher powder charge with shorter brass and see if that was a contributor. The Sammi case length is 2.280” and my trimmer was only trimming to 2.275”. It’s easy enough to shorten the case length gage. I’m now at 2.263” which is still longer than the 2.260” minimum.
Click to expand...

So you reduced the load by half a grain and the problem went away? Wow!
 
#34
918v said:
So you reduced the load by half a grain and the problem went away? Wow!
Click to expand...
I also shortened the trim length 0.012”. I’m gonna go back to the original 62 grain charge (+0.5grain from 61.5) with the reduced trim length and see if the problem is still gone. My fired case lengths are at 2.280”, which is the Sammi length. Since I full length resize I’m ensuring the shoulder is not too far forward.
 
#35
I also measured all my fired cases to be 0.533” at the 0.200 line above the base. This is where the AW2 reamer starts increasing the chamber ID from 0.533” to 0.535”. I have not heard back from Seekins yet (email) asking if they already use the AW2 reamer. If the brass expands to the chamber wall and then relaxes back some amount, it seems like I can assume the chamber must be >0.533”. The Sammi case dimension at base is 0.532” so there is only 0.001” clearance with the AW2 reamer. I have no idea if the additional case trim shortening will help, but I’ll find out. My 2.263” trimmed cases lengthened to 2.271” after firing. So I’m getting 0.008” lengthening from 1 firing. That could have been an issue starting from 2.275” which is what my trimmer was producing. Some load data suggests trimming to 2.270”.
 
#37
rmiked said:
The base of the fired cartridge is 0.530” before and after firing, not really changing.
Click to expand...

rmiked said:
I also measured all my fired cases to be 0.533” at the 0.200 line above the base.
Click to expand...

So the first measurement was incorrect and your brass is really expanding to .533”? And your FL sizer takes it down to .530”?

If so, then it’s not the chamber and the only problem was the excessive pressure which you fixed by dropping the charge weight.
 
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#38
No it appears to be 0.530” at the bottom of base and 0.533” up an amount of 0.200”. Makes sense it’s very stiff at the case head. I’ve never taken so many measurements but never had this issue. But the AW2 reamer description is specific about being 0.200 above the base. I’m not referring to the plane containing the primer bottom. When I say bottom of base I am measuring immediately above the extractor slot in the case rim.
 
#39
rmiked said:
No it appears to be 0.530” at the bottom of base and 0.533” up an amount of 0.200”. Makes sense it’s very stiff at the case head. I’ve never taken so many measurements but never had this issue. But the AW2 reamer description is specific about being 0.200 above the base. I’m not referring to the plane containing the primer bottom. When I say bottom of base I am measuring immediately above the extractor slot in the case rim.
Click to expand...

That part of the base doesn’t really change. The important part is the expanded area above. What does that measure after sizing?
 
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#40
0.533”. So if it relaxed any, like from 0.535” down to 0.533, then my issue is likely powder charge. Assuming you are correct that trim length is not a contributor.
 

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#41
Is it possible a 1/2 grain reduction could make a sticky bolt go away? Still wondering why I can’t load max charge without an issue. Which is why I may order some ADG brass. Once I get done with these tests.
 
#42
rmiked said:
Is it possible a 1/2 grain reduction could make a sticky bolt go away? Still wondering why I can’t load max charge without an issue. Which is why I may order some ADG brass. Once I get done with these tests.
Click to expand...

Yes because it reduces pressure which is the cause of sticky bolt. Some brands of brass are softer than others and cannot take the same pressure. So the smart person reduces the powder charge and runs the lower accuracy node with that brass.

Just because your powder charge is below published max doesn’t mean your pressure is below max. It could be but probably isn’t as evidenced by your sticky bolt.

Just because you are able to run a higher powder charge in a harder case doesn’t mean you’re below max either. You are probably above max pressure just that the case can take it because it’s stronger than a softer case.
 
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#43
Did you lube up your chamber or brass? If you're seeing ejector marks, it could be overpressure, but more directly you're seeing high bolt thrust (which also isn't great). The brass gets extruded into the ejector pocket and you have to roll or shave that over to rotate the bolt. Thus the heavy lift. That can happen with safe pressures if your chamber is really slick and lubed up (or with oily brass). It can also be affected by how sharp the ejector/hole is and the tolerances on the ejector pocket itself. Also affected by how hard the brass is at the base.

Load could also just be too damn pissin hot.
 
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#44
Yeah, lube or wax on the cases left over from the reloading process can cause this issue also and should always be removed thoroughly to eliminate this variable
 
#45
And for reference

There is no guarantee that any particular rifle will safely achieve max pressure and velocity.

You are only one step below max in the published Hornady data, so maybe you just have a tight bore or one that has higher friction and does not allow you to achieve the maximum published velocities

Somebody has to have such a rifle, else we would not need to publish a range of charges. We would just publish the maximum and it would suit everyone and every rifle.
IMG_7325.png
 
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#46
rmiked said:
Is it possible a 1/2 grain reduction could make a sticky bolt go away? Still wondering why I can’t load max charge without an issue. Which is why I may order some ADG brass. Once I get done with these tests.
Click to expand...
Hornady brass is soft.

Sorry if I miss it are you chrono-ing these loads?

ADG brass tends to be thicker so the 1/2 grain down you are running now may well give you your max velocity and pressure. It should be faster than the hornady brass, all things being equal….
 
#47
I do not have a chrono but have shot (175 ELDX) at 100 and 200 yards and inferred velocity using Hornady ballistic App. After inputting the correct scope height and other parameters, the App shows when zeroed at 200 yds, the round is 1.4” high at 100 yds. That trajectory reconciles with a velocity of 2875 ft/sec. It groups well (0.5 MOA or less) at 100 and 200 yds for 3 shot groups. I noticed the groups are smaller and more consistent with hand loads vs Hornady factory loads. I have a Seekins muzzle brake on it that came with my SP10 (don’t use on SP10 as it’s 6.5 Creedmoor) and is low recoil because the rifle is heavy. The Havak 7 PRC (26” barrel) is very pleasant recoil with the muzzle brake installed. I am fine with 2875 ft/sec as it should be easier on barrel and is about 47 % more energy than my 6.5 Creedmoor shooting 140 grain bullets.
 
#48
You need a chronograph.

I appreciate what you were trying to do, but there is far too much measurement error in the method you propose to be able to estimate your velocity by a difference in impact between 100 and 200 yards

You might be right, but you would get just as close from guessing any velocity within 50 to 100 ft./s of 2900
 
#49
rmiked said:
I do not have a chrono but have shot (175 ELDX) at 100 and 200 yards and inferred velocity using Hornady ballistic App. After inputting the correct scope height and other parameters, the App shows when zeroed at 200 yds, the round is 1.4” high at 100 yds. That trajectory reconciles with a velocity of 2875 ft/sec. It groups well (0.5 MOA or less) at 100 and 200 yds for 3 shot groups. I noticed the groups are smaller and more consistent with hand loads vs Hornady factory loads. I have a Seekins muzzle brake on it that came with my SP10 (don’t use on SP10 as it’s 6.5 Creedmoor) and is low recoil because the rifle is heavy. The Havak 7 PRC (26” barrel) is very pleasant recoil with the muzzle brake installed. I am fine with 2875 ft/sec as it should be easier on barrel and is about 47 % more energy than my 6.5 Creedmoor shooting 140 grain bullets.
Click to expand...

Can you borrow a chrono? I agree that at this point you really need to chrono.

BTW I have quickload, so I can run some numbers for you but to fine tune, I really will need those chrono numbers.
 
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